read-cache: convert to struct object_id

Replace hashcmp with oidcmp.

Signed-off-by: Patryk Obara <patryk.obara@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

read-cache.c

@@ -160,9 +160,9 @@ static int ce_compare_data(const struct cache_entry *ce, struct stat *st)
 	int fd = git_open_cloexec(ce->name, O_RDONLY);
 
 	if (fd >= 0) {
-		unsigned char sha1[20];
-		if (!index_fd(sha1, fd, st, OBJ_BLOB, ce->name, 0))
-			match = hashcmp(sha1, ce->oid.hash);
+		struct object_id oid;
+		if (!index_fd(oid.hash, fd, st, OBJ_BLOB, ce->name, 0))
+			match = oidcmp(&oid, &ce->oid);
 		/* index_fd() closed the file descriptor already */
 	}
 	return match;