'destroy_workqueue()' already drains the queue before destroying it, so
there is no need to flush it explicitly.
Remove the redundant 'flush_workqueue()' calls.
Signed-off-by: Xu Wang <vulab@iscas.ac.cn> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>