video: don't use flush_scheduled_work() in fb_defio

flush_scheduled_work() in on the way out.  fb_deferred_io_cleanup()
can simply sync-cancel info->deferred_work instead of cancel +
flush_scheduled_work().  Drop flush_scheduled_work() usage.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jaya Kumar <jayalk@intworks.biz>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>