submodule.c: use the ARRAY_SIZE macro

Use the ARRAY_SIZE macro to get the number
of elements in an array.
Signed-off-by: NElia Pinto <gitter.spiros@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

submodule.c

@@ -965,7 +965,7 @@ static int find_first_merges(struct object_array *result, const char *path,
 			sha1_to_hex(a->object.sha1));
 	init_revisions(&revs, NULL);
 	rev_opts.submodule = path;
-	setup_revisions(sizeof(rev_args)/sizeof(char *)-1, rev_args, &revs, &rev_opts);
+	setup_revisions(ARRAY_SIZE(rev_args)-1, rev_args, &revs, &rev_opts);
 
 	/* save all revisions from the above list that contain b */
 	if (prepare_revision_walk(&revs))