Remove a few redundant memset after calloc.

Using the following semantic patch provided by Mansour Moufid:

@@
expression x;
@@
  x = mbedtls_calloc(...)
  ...
- memset(x, 0, ...);

library/asn1parse.c

@@ -275,8 +275,6 @@ int mbedtls_asn1_get_sequence_of( unsigned char **p,
             if( cur->next == NULL )
                 return( MBEDTLS_ERR_ASN1_MALLOC_FAILED );
 
-            memset( cur->next, 0, sizeof( mbedtls_asn1_sequence ) );
-
             cur = cur->next;
         }
     }