rnbd: add error handling support for add_disk()

We never checked for errors on add_disk() as this function
returned void. Now that this is fixed, use the shiny new
error handling.

Acked-by: Jack Wang <[e-mail]>
Signed-off-by: Luis Chamberlain <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

drivers/block/rnbd/rnbd-clt.c

···
 	blk_queue_write_cache(dev->queue, dev->wc, dev->fua);
 }
 
-static void rnbd_clt_setup_gen_disk(struct rnbd_clt_dev *dev, int idx)
+static int rnbd_clt_setup_gen_disk(struct rnbd_clt_dev *dev, int idx)
 {
+	int err;
+
 	dev->gd->major		= rnbd_client_major;
 	dev->gd->first_minor	= idx << RNBD_PART_BITS;
 	dev->gd->minors		= 1 << RNBD_PART_BITS;
···
 
 	if (!dev->rotational)
 		blk_queue_flag_set(QUEUE_FLAG_NONROT, dev->queue);
-	add_disk(dev->gd);
+	err = add_disk(dev->gd);
+	if (err)
+		blk_cleanup_disk(dev->gd);
+
+	return err;
 }
 
 static int rnbd_client_setup_device(struct rnbd_clt_dev *dev)
···
 	rnbd_init_mq_hw_queues(dev);
 
 	setup_request_queue(dev);
-	rnbd_clt_setup_gen_disk(dev, idx);
-	return 0;
+	return rnbd_clt_setup_gen_disk(dev, idx);
 }
 
 static struct rnbd_clt_dev *init_dev(struct rnbd_clt_session *sess,