media/video: don't use flush_scheduled_work()

This patch converts the remaining users of flush_scheduled_work() in
media/video.

* bttv-input.c and cx23885-input.c don't use workqueue at all.  No
  need to flush.

* Make omap24xxcam.c and saa7134-empress.c flush the used work
  directly.

* In fd_defio.c, replace cancel_delayed_work() +
  flush_scheduled_work() with cancel_delayed_work_sync().  While at
  it, replace the deprecated cancel_rearming_delayed_work() with
  cancel_delayed_work_sync().

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>