If blk_mq_init_queue() fails, it should return error code in ublk_add_dev()

Fixes: cebbe577 ("ublk_drv: fix request queue leak")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20220718042408.3132835-1-yangyingliang@huawei.comSigned-off-by: Jens Axboe <axboe@kernel.dk>