hcrypto: Use correct size for memset in md2

md2.c was doing memset(m, 0, sizeof(m)), and so was only clearing
the first 4 bytes of the passed md2 structure in MD2_Final. Fix
this to clear the entire structure, as expected.

lib/hcrypto/md2.c

@@ -130,5 +130,5 @@ MD2_Final (void *res, struct md2 *m)
     MD2_Update(m, pad, 16);
 
     memcpy(res, m->state, MD2_DIGEST_LENGTH);
-    memset(m, 0, sizeof(m));
+    memset(m, 0, sizeof(*m));
 }