CIFS: Simplify invalidate part (try #5)

Simplify many places when we call cifs_revalidate/invalidate to make
it do what it exactly needs.

Reviewed-by: Jeff Layton <jlayton@samba.org>
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>