block: add WARN_ON if bdi register fail

device_add_disk need do more safety error handle, so this patch just
add WARN_ON.
Reviewed-by: NJan Kara <jack@suse.cz>
Signed-off-by: Nweiping zhang <zhangweiping@didichuxing.com>

Adapted for current series by me.
Signed-off-by: NJens Axboe <axboe@kernel.dk>

block/genhd.c

@@ -671,10 +671,13 @@ void device_add_disk(struct device *parent, struct gendisk *disk)
 		disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
 		disk->flags |= GENHD_FL_NO_PART_SCAN;
 	} else {
+		int ret;
+
 		/* Register BDI before referencing it from bdev */
 		disk_to_dev(disk)->devt = devt;
-		bdi_register_owner(disk->queue->backing_dev_info,
-				disk_to_dev(disk));
+		ret = bdi_register_owner(disk->queue->backing_dev_info,
+						disk_to_dev(disk));
+		WARN_ON(ret);
 		blk_register_region(disk_devt(disk), disk->minors, NULL,
 				    exact_match, exact_lock, disk);
 	}