Use plain memset() for freshly allocated objects

This commits reverts to plain memset() for cases like:

    some_type foo;
    memset( &foo, 0, sizeof( foo ) );

(Sometimes there is code between declaration in memset(), but it doesn't
matter as long as it doesn't touch foo.)

The reasoning is the same as in the previous commit: the stack shouldn't
contain sensitive data as we carefully wipe it after use.
diff --git a/library/asn1parse.c b/library/asn1parse.c
index ac3943a..990ae38 100644
--- a/library/asn1parse.c
+++ b/library/asn1parse.c
@@ -391,7 +391,7 @@
     int ret;
     mbedtls_asn1_buf params;
 
-    mbedtls_platform_memset( &params, 0, sizeof(mbedtls_asn1_buf) );
+    memset( &params, 0, sizeof(mbedtls_asn1_buf) );
 
     if( ( ret = mbedtls_asn1_get_alg( p, end, alg, &params ) ) != 0 )
         return( ret );