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/md2.c b/library/md2.c
index 1c0b3df..82aed8e 100644
--- a/library/md2.c
+++ b/library/md2.c
@@ -35,6 +35,7 @@
 
 #include "mbedtls/md2.h"
 #include "mbedtls/platform_util.h"
+#include "mbedtls/error.h"
 
 #include <string.h>
 
@@ -170,7 +171,7 @@
                             const unsigned char *input,
                             size_t ilen )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t fill;
 
     while( ilen > 0 )
@@ -212,7 +213,7 @@
 int mbedtls_md2_finish_ret( mbedtls_md2_context *ctx,
                             unsigned char output[16] )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t i;
     unsigned char x;
 
@@ -250,7 +251,7 @@
                      size_t ilen,
                      unsigned char output[16] )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     mbedtls_md2_context ctx;
 
     mbedtls_md2_init( &ctx );