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/pkcs5.c b/library/pkcs5.c
index 3d29fd7..8832322 100644
--- a/library/pkcs5.c
+++ b/library/pkcs5.c
@@ -38,6 +38,7 @@
 #if defined(MBEDTLS_PKCS5_C)
 
 #include "mbedtls/pkcs5.h"
+#include "mbedtls/error.h"
 
 #if defined(MBEDTLS_ASN1_PARSE_C)
 #include "mbedtls/asn1.h"
@@ -59,7 +60,7 @@
                                       mbedtls_asn1_buf *salt, int *iterations,
                                       int *keylen, mbedtls_md_type_t *md_type )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     mbedtls_asn1_buf prf_alg_oid;
     unsigned char *p = params->p;
     const unsigned char *end = params->p + params->len;