mdp_get_plat_device() was added in 2022 but has remained unused.
Remove it.
Fixes: 61890ccaefaf ("media: platform: mtk-mdp3: add MediaTek MDP3 driver") Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org> Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com> Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com> Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>