media: mtk-vcodec: venc: set OUTPUT buffers field to V4L2_FIELD_NONE

A default value of 0 means V4L2_FIELD_ANY, which is not correct.
Reported by v4l2-compliance.

Signed-off-by: Alexandre Courbot <acourbot@chromium.org>
Acked-by: Tiffany Lin <tiffany.lin@mediatek.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>