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/crypto/LPdir_vms.c b/crypto/LPdir_vms.c
index 1e8f9e7..362918d 100644
--- a/crypto/LPdir_vms.c
+++ b/crypto/LPdir_vms.c
@@ -109,7 +109,7 @@
             errno = ENOMEM;
             return 0;
         }
-        memset(*ctx, '\0', sizeof(**ctx));
+        memset(*ctx, 0, sizeof(**ctx));
 
         strcpy((*ctx)->filespec, directory);
         strcat((*ctx)->filespec, "*.*;");