Input: atkbd - cancel delayed work before freeing its structure

Pointed out by Oleg Nesterov. Since delayed work is used here, use of
flush_scheduled_work() is not sufficient in atkbd_disconnect(). It does
not wait for scheduled delayed work to finish. This patch prevents
delayed work to be processed after freeing atkbd structure (used struct
delayed_work is part of atkbd) by cancelling this delayed work.

Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>