list: use list_count_nodes() to count list entries

Use the API function list_count_nodes() to count the number of list
entries.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/scene.c b/boot/scene.c
index ac976aa..270c9c6 100644
--- a/boot/scene.c
+++ b/boot/scene.c
@@ -79,13 +79,7 @@
 
 int scene_obj_count(struct scene *scn)
 {
-	struct scene_obj *obj;
-	int count = 0;
-
-	list_for_each_entry(obj, &scn->obj_head, sibling)
-		count++;
-
-	return count;
+	return list_count_nodes(&scn->obj_head);
 }
 
 void *scene_obj_find(const struct scene *scn, uint id, enum scene_obj_t type)