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/ssl/d1_msg.c b/ssl/d1_msg.c
index f71b1cc..13bda46 100644
--- a/ssl/d1_msg.c
+++ b/ssl/d1_msg.c
@@ -161,7 +161,7 @@
 
     s->s3->alert_dispatch = 0;
 
-    memset(buf, 0x00, sizeof(buf));
+    memset(buf, 0, sizeof(buf));
     *ptr++ = s->s3->send_alert[0];
     *ptr++ = s->s3->send_alert[1];