[media] af9013: cancel_delayed_work_sync before device removal / kfree

af9013_remove  was calling  kfree(state)  with  possibly still  active
schedule_delayed_work(&state->statistics_work).   A   similar  bug  in
si2157 caused kernel panics in call_timer_fn e.g. after rmmod cx23885.

Signed-off-by: Ernst Martin Witte <emw-linux-kernel@nocabal.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>