media: vim2m: use cancel_delayed_work_sync instead of flush_schedule_work

The use of flush_schedule_work() made no sense and caused a syzkaller error.
Replace with the correct cancel_delayed_work_sync().

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reported-by:  <syzbot+69780d144754b8071f4b@syzkaller.appspotmail.com>
Cc: <stable@vger.kernel.org>      # for v4.20 and up
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>