memset, memcpy, sizeof consistency fixes

Just as with the OPENSSL_malloc calls, consistently use sizeof(*ptr)
for memset and memcpy.  Remove needless casts for those functions.
For memset, replace alternative forms of zero with 0.

Reviewed-by: Richard Levitte <levitte@openssl.org>
diff --git a/test/enginetest.c b/test/enginetest.c
index 2d9afaa..54e6ead 100644
--- a/test/enginetest.c
+++ b/test/enginetest.c
@@ -119,7 +119,7 @@
     CRYPTO_mem_ctrl(CRYPTO_MEM_CHECK_ON);
     ERR_load_crypto_strings();
 
-    memset(block, 0, 512 * sizeof(ENGINE *));
+    memset(block, 0, sizeof(block));
     if (((new_h1 = ENGINE_new()) == NULL) ||
         !ENGINE_set_id(new_h1, "test_id0") ||
         !ENGINE_set_name(new_h1, "First test item") ||