dm rq: check blk_mq_register_dev() return value in dm_mq_init_request_queue()

Otherwise the request-based DM blk-mq request_queue will be put into
service without being properly exported via sysfs.

Cc: [e-mail]
Signed-off-by: Bart Van Assche <[e-mail]>
Reviewed-by: Hannes Reinecke <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Signed-off-by: Mike Snitzer <[e-mail]>

drivers/md/dm-rq.c

···
 	dm_init_md_queue(md);
 
 	/* backfill 'mq' sysfs registration normally done in blk_register_queue */
-	blk_mq_register_dev(disk_to_dev(md->disk), q);
+	err = blk_mq_register_dev(disk_to_dev(md->disk), q);
+	if (err)
+		goto out_cleanup_queue;
 
 	return 0;
 
+out_cleanup_queue:
+	blk_cleanup_queue(q);
 out_tag_set:
 	blk_mq_free_tag_set(md->tag_set);
 out_kfree_tag_set: