media: v4l: Use memset_after() helper

The CLEAR_AFTER_FIELD defined here is functionally the same as
memset_after() helper, so replace it with memset_after() to simplify the
code, no functional change in this patch.

Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>