rbd: add add_disk() error handling

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

Signed-off-by: Luis Chamberlain <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/block/rbd.c

···
 	if (rc)
 		goto err_out_image_lock;
 
-	device_add_disk(&rbd_dev->dev, rbd_dev->disk, NULL);
+	rc = device_add_disk(&rbd_dev->dev, rbd_dev->disk, NULL);
+	if (rc)
+		goto err_out_cleanup_disk;
 
 	spin_lock(&rbd_dev_list_lock);
 	list_add_tail(&rbd_dev->node, &rbd_dev_list);
···
 	module_put(THIS_MODULE);
 	return rc;
 
+err_out_cleanup_disk:
+	rbd_free_disk(rbd_dev);
 err_out_image_lock:
 	rbd_dev_image_unlock(rbd_dev);
 	rbd_dev_device_release(rbd_dev);