ksmbd: make smb2_find_context_vals return NULL if not found

mainline inclusion
from mainline-5.15-rc1
commit ce154c32
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I60T7G
CVE: NA

Reference: https://git.kernel.org/torvalds/linux/c/ce154c32af3c



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instead of -ENOENT, make smb2_find_context_vals
return NULL if the given context cannot be found.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hyunchul Lee <hyc.lee@gmail.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>