[media] vcodec: mediatek: add Maintainers entry for Mediatek MT8173 vcodec drivers

Add Tiffany Lin and Andrew-CT Chen as maintainers for
Mediatek MT8173 vcodec drivers

Signed-off-by: Tiffany Lin <tiffany.lin@mediatek.com>
Signed-off-by: Andrew-CT Chen <andrew-ct.chen@mediatek.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>