ublk: pass NULL to blk_mq_alloc_disk() as queuedata

queuedata is not referenced in ublk_drv and we can use driver_data
instead. Pass NULL to blk_mq_alloc_disk() as queuedata while allocating
ublk's gendisk.
Signed-off-by: Ziyang Zhang <ZiyangZhang@linux.alibaba.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230207070839.370817-4-ZiyangZhang@linux.alibaba.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/ublk_drv.c

@@ -1578,7 +1578,7 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub, struct io_uring_cmd *cmd)
 		goto out_unlock;
 	}
 
-	disk = blk_mq_alloc_disk(&ub->tag_set, ub);
+	disk = blk_mq_alloc_disk(&ub->tag_set, NULL);
 	if (IS_ERR(disk)) {
 		ret = PTR_ERR(disk);
 		goto out_unlock;