mm/backing-dev.c: use rb_entry()

To make the code clearer, use rb_entry() instead of container_of() to
deal with rbtree.

Link: http://lkml.kernel.org/r/671275de093d93ddc7c6f77ddc0d357149691a39.1484306840.git.geliangtang@gmail.comSigned-off-by: NGeliang Tang <geliangtang@gmail.com>
Cc: Jens Axboe <axboe@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/backing-dev.c

@@ -411,8 +411,8 @@ wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
 
 	while (*node != NULL) {
 		parent = *node;
-		congested = container_of(parent, struct bdi_writeback_congested,
-					 rb_node);
+		congested = rb_entry(parent, struct bdi_writeback_congested,
+				     rb_node);
 		if (congested->blkcg_id < blkcg_id)
 			node = &parent->rb_left;
 		else if (congested->blkcg_id > blkcg_id)