cifs: remove unused variable 'server'

Fix build warning by removing unused variable 'server':

fs/cifs/inode.c:1089:26: warning:
 variable server set but not used [-Wunused-but-set-variable]
 1089 |  struct TCP_Server_Info *server;
      |                          ^~~~~~

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>