nbd: Fix debugfs_create_dir error checking

stable inclusion
from stable-v5.10.183
commit 01c3d3064975944a2edefef6e2f99db3244ca999
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7FF4R

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=01c3d3064975944a2edefef6e2f99db3244ca999



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[ Upstream commit 4913cfcf ]

The debugfs_create_dir function returns ERR_PTR in case of error, and the
only correct way to check if an error occurred is 'IS_ERR' inline function.
This patch will replace the null-comparison with IS_ERR.

Signed-off-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Link: https://lore.kernel.org/r/20230512130533.98709-1-ivan.orlov0322@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zhong Jinghua <zhongjinghua@huaweicloud.com>