rbd: avoid format-security warning inside alloc_workqueue()

drivers/block/rbd.c: In function ‘rbd_dev_device_setup’:
drivers/block/rbd.c:5090:19: warning: format not a string literal and no format arguments [-Wformat-security]

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>

drivers/block/rbd.c

@@ -5087,7 +5087,7 @@ static int rbd_dev_device_setup(struct rbd_device *rbd_dev)
 	set_capacity(rbd_dev->disk, rbd_dev->mapping.size / SECTOR_SIZE);
 	set_disk_ro(rbd_dev->disk, rbd_dev->mapping.read_only);
 
-	rbd_dev->rq_wq = alloc_workqueue(rbd_dev->disk->disk_name, 0, 0);
+	rbd_dev->rq_wq = alloc_workqueue("%s", 0, 0, rbd_dev->disk->disk_name);
 	if (!rbd_dev->rq_wq)
 		goto err_out_mapping;