block: Use pointer to backing_dev_info from request_queue

We will want to have struct backing_dev_info allocated separately from
struct request_queue. As the first step add pointer to backing_dev_info
to request_queue and convert all users touching it. No functional
changes in this patch.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index ff4a29a..9e958bc 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1313,7 +1313,7 @@ static int dm_any_congested(void *congested_data, int bdi_bits)
 			 * With request-based DM we only need to check the
 			 * top-level queue for congestion.
 			 */
-			r = md->queue->backing_dev_info.wb.state & bdi_bits;
+			r = md->queue->backing_dev_info->wb.state & bdi_bits;
 		} else {
 			map = dm_get_live_table_fast(md);
 			if (map)
@@ -1396,7 +1396,7 @@ void dm_init_md_queue(struct mapped_device *md)
 	 * - must do so here (in alloc_dev callchain) before queue is used
 	 */
 	md->queue->queuedata = md;
-	md->queue->backing_dev_info.congested_data = md;
+	md->queue->backing_dev_info->congested_data = md;
 }
 
 void dm_init_normal_md_queue(struct mapped_device *md)
@@ -1407,7 +1407,7 @@ void dm_init_normal_md_queue(struct mapped_device *md)
 	/*
 	 * Initialize aspects of queue that aren't relevant for blk-mq
 	 */
-	md->queue->backing_dev_info.congested_fn = dm_any_congested;
+	md->queue->backing_dev_info->congested_fn = dm_any_congested;
 	blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
 }