ksmbd: fix unused err value in smb2_lock

mainline inclusion
from mainline-5.15-rc1
commit 96ad4ec5
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I60T7G
CVE: NA

Reference: https://git.kernel.org/torvalds/linux/c/96ad4ec51c06



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

CID 1502845 (#1 of 1): Unused value (UNUSED_VALUE)
value_overwrite: Overwriting previous write to err with value from
vfs_lock_file(filp, 0U, rlock, NULL).
6880                err = vfs_lock_file(filp, 0, rlock, NULL);
6881                if (err)
6882                        pr_err("rollback unlock fail : %d\n", err);

Reported-by: Coverity Scan <scan-admin@coverity.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Zhong Jinghua <zhongjinghua@huawei.com>