Initialise return values to an error

Initialising the return values to and error is best practice and makes
the library more robust.
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index b98a462..c82cae9 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -75,6 +75,7 @@
 #include "mbedtls/pk.h"
 #include "mbedtls/pk_internal.h"
 #include "mbedtls/platform_util.h"
+#include "mbedtls/error.h"
 #include "mbedtls/ripemd160.h"
 #include "mbedtls/rsa.h"
 #include "mbedtls/sha1.h"
@@ -1147,7 +1148,7 @@
     psa_key_attributes_t *attributes )
 {
     mbedtls_mpi mpi;
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     uint8_t *buffer = NULL;
     size_t buflen;
     mbedtls_mpi_init( &mpi );
@@ -1251,7 +1252,7 @@
 static int pk_write_pubkey_simple( mbedtls_pk_context *key,
                                    unsigned char *buf, size_t size )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     unsigned char *c;
     size_t len = 0;
 
@@ -1336,7 +1337,7 @@
             PSA_KEY_TYPE_IS_ECC( slot->attr.type ) )
         {
             mbedtls_pk_context pk;
-            int ret;
+            int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
             if( PSA_KEY_TYPE_IS_RSA( slot->attr.type ) )
             {
 #if defined(MBEDTLS_RSA_C)
@@ -1784,7 +1785,7 @@
         if( PSA_KEY_TYPE_IS_RSA( slot->attr.type ) )
         {
             mbedtls_mpi actual, required;
-            int ret;
+            int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
             mbedtls_mpi_init( &actual );
             mbedtls_mpi_init( &required );
             ret = mbedtls_rsa_export( slot->data.rsa,
@@ -2107,7 +2108,7 @@
 psa_status_t psa_hash_setup( psa_hash_operation_t *operation,
                              psa_algorithm_t alg )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
 
     /* A context must be freshly initialized before it can be set up. */
     if( operation->alg != 0 )
@@ -2183,7 +2184,7 @@
                               const uint8_t *input,
                               size_t input_length )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
 
     /* Don't require hash implementations to behave correctly on a
      * zero-length input, which may have an invalid pointer. */
@@ -2251,7 +2252,7 @@
                               size_t *hash_length )
 {
     psa_status_t status;
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t actual_hash_length = PSA_HASH_SIZE( operation->alg );
 
     /* Fill the output buffer with something that isn't a valid hash
@@ -2634,7 +2635,7 @@
                            psa_key_slot_t *slot,
                            const mbedtls_cipher_info_t *cipher_info )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
 
     operation->mac_size = cipher_info->block_size;
 
@@ -2755,7 +2756,7 @@
         const mbedtls_cipher_info_t *cipher_info =
             mbedtls_cipher_info_from_psa( full_length_alg,
                                           slot->attr.type, key_bits, NULL );
-        int ret;
+        int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
         if( cipher_info == NULL )
         {
             status = PSA_ERROR_NOT_SUPPORTED;
@@ -3107,7 +3108,7 @@
                                   size_t *signature_length )
 {
     psa_status_t status;
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     mbedtls_md_type_t md_alg;
 
     status = psa_rsa_decode_md_type( alg, hash_length, &md_alg );
@@ -3165,7 +3166,7 @@
                                     size_t signature_length )
 {
     psa_status_t status;
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     mbedtls_md_type_t md_alg;
 
     status = psa_rsa_decode_md_type( alg, hash_length, &md_alg );
@@ -3231,7 +3232,7 @@
                                     size_t signature_size,
                                     size_t *signature_length )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     mbedtls_mpi r, s;
     size_t curve_bytes = PSA_BITS_TO_BYTES( ecp->grp.pbits );
     mbedtls_mpi_init( &r );
@@ -3286,7 +3287,7 @@
                                       const uint8_t *signature,
                                       size_t signature_length )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     mbedtls_mpi r, s;
     size_t curve_bytes = PSA_BITS_TO_BYTES( ecp->grp.pbits );
     mbedtls_mpi_init( &r );
@@ -3525,7 +3526,7 @@
     if( PSA_KEY_TYPE_IS_RSA( slot->attr.type ) )
     {
         mbedtls_rsa_context *rsa = slot->data.rsa;
-        int ret;
+        int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
         if( output_size < mbedtls_rsa_get_len( rsa ) )
             return( PSA_ERROR_BUFFER_TOO_SMALL );
 #if defined(MBEDTLS_PKCS1_V15)
@@ -3604,7 +3605,7 @@
     if( slot->attr.type == PSA_KEY_TYPE_RSA_KEY_PAIR )
     {
         mbedtls_rsa_context *rsa = slot->data.rsa;
-        int ret;
+        int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
 
         if( input_length != mbedtls_rsa_get_len( rsa ) )
             return( PSA_ERROR_INVALID_ARGUMENT );
@@ -3801,7 +3802,7 @@
                                      size_t *iv_length )
 {
     psa_status_t status;
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     if( operation->iv_set || ! operation->iv_required )
     {
         return( PSA_ERROR_BAD_STATE );
@@ -3833,7 +3834,7 @@
                                 size_t iv_length )
 {
     psa_status_t status;
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     if( operation->iv_set || ! operation->iv_required )
     {
         return( PSA_ERROR_BAD_STATE );
@@ -3861,7 +3862,7 @@
                                 size_t *output_length )
 {
     psa_status_t status;
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t expected_output_size;
 
     if( operation->alg == 0 )
@@ -5371,7 +5372,7 @@
 psa_status_t psa_generate_random( uint8_t *output,
                                   size_t output_size )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     GUARD_MODULE_INITIALIZED;
 
     while( output_size > MBEDTLS_CTR_DRBG_MAX_REQUEST )
@@ -5466,7 +5467,7 @@
     if ( type == PSA_KEY_TYPE_RSA_KEY_PAIR )
     {
         mbedtls_rsa_context *rsa;
-        int ret;
+        int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
         int exponent;
         psa_status_t status;
         if( bits > PSA_VENDOR_RSA_MAX_KEY_BITS )
@@ -5508,7 +5509,7 @@
         const mbedtls_ecp_curve_info *curve_info =
             mbedtls_ecp_curve_info_from_grp_id( grp_id );
         mbedtls_ecp_keypair *ecp;
-        int ret;
+        int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
         if( domain_parameters_size != 0 )
             return( PSA_ERROR_NOT_SUPPORTED );
         if( grp_id == MBEDTLS_ECP_DP_NONE || curve_info == NULL )