ksmbd: fix missing error code in smb2_lock

Dan report a warning that is missing error code in smb2_lock
from static checker. This patch add error code to avoid static checker
warning.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>