[media] ivtv: ivtv-driver: Replace 'flush_work_sync()'

Since commit 43829731 (workqueue: deprecate flush[_delayed]_work_sync()),
flush_work() should be used instead of flush_work_sync().

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>