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>

crypto/LPdir_win.c

@@ -74,7 +74,7 @@ const char *LP_find_file(LP_DIR_CTX **ctx, const char *directory)
             errno = ENOMEM;
             return 0;
         }
-        memset(*ctx, '\0', sizeof(**ctx));
+        memset(*ctx, 0, sizeof(**ctx));
 
         if (directory[dirlen - 1] != '*') {
             extdirbuf = (char *)malloc(dirlen + 3);