nbd: fix possible overflow for 'first_minor' in nbd_dev_add()

stable inclusion
from stable-v5.10.170
commit 2e0c3e43ebb99c2b495229f8fade4c043fbd06a5
category: bugfix
bugzilla: 188217

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2e0c3e43ebb99c2b495229f8fade4c043fbd06a5



----------------------------------------

commit 940c2649 upstream.

If 'part_shift' is not zero, then 'index << part_shift' might
overflow to a value that is not greater than '0xfffff', then sysfs
might complains about duplicate creation.

Fixes: b0d9111a ("nbd: use an idr to keep track of nbd devices")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20211102015237.2309763-3-yebin10@huawei.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Wen Yang <wenyang.linux@foxmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zhong Jinghua <zhongjinghua@huawei.com>
Signed-off-by: Li Nan <linan122@huawei.com>