Use safer sizeof variant in malloc

For a local variable:
        TYPE *p;
Allocations like this are "risky":
        p = OPENSSL_malloc(sizeof(TYPE));
if the type of p changes, and the malloc call isn't updated, you
could get memory corruption.  Instead do this:
        p = OPENSSL_malloc(sizeof(*p));
Also fixed a few memset() calls that I noticed while doing this.

Reviewed-by: Richard Levitte <levitte@openssl.org>

crypto/engine/eng_table.c

@@ -147,7 +147,7 @@ int engine_table_register(ENGINE_TABLE **table, ENGINE_CLEANUP_CB *cleanup,
         tmplate.nid = *nids;
         fnd = lh_ENGINE_PILE_retrieve(&(*table)->piles, &tmplate);
         if (!fnd) {
-            fnd = OPENSSL_malloc(sizeof(ENGINE_PILE));
+            fnd = OPENSSL_malloc(sizeof(*fnd));
             if (!fnd)
                 goto end;
             fnd->uptodate = 1;