cifs: Remove useless variable

Fix the following gcc warning:

fs/cifs/cifsacl.c:1097:8: warning: variable ‘nmode’ set but not used
[-Wunused-but-set-variable].

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Steve French <stfrench@microsoft.com>