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/ripemd160.c b/library/ripemd160.c
index 0791ae4..a62f4b8 100644
--- a/library/ripemd160.c
+++ b/library/ripemd160.c
@@ -35,6 +35,7 @@
 
 #include "mbedtls/ripemd160.h"
 #include "mbedtls/platform_util.h"
+#include "mbedtls/error.h"
 
 #include <string.h>
 
@@ -322,7 +323,7 @@
                                   const unsigned char *input,
                                   size_t ilen )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t fill;
     uint32_t left;
 
@@ -390,7 +391,7 @@
 int mbedtls_ripemd160_finish_ret( mbedtls_ripemd160_context *ctx,
                                   unsigned char output[20] )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     uint32_t last, padn;
     uint32_t high, low;
     unsigned char msglen[8];
@@ -439,7 +440,7 @@
                            size_t ilen,
                            unsigned char output[20] )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     mbedtls_ripemd160_context ctx;
 
     mbedtls_ripemd160_init( &ctx );