[media] vcodec: mediatek: Add Maintainers entry for Mediatek JPEG driver

Signed-off-by: Rick Chang <rick.chang@mediatek.com>
Signed-off-by: Minghsiu Tsai <minghsiu.tsai@mediatek.com>
Signed-off-by: Bin Liu <bin.liu@mediatek.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>