MAINTAINERS: adjust file entry in MEDIATEK MDP DRIVER

MAINTAINERS: adjust file entry in MEDIATEK MDP DRIVER

Commit fbf97d6c1dd4 ("dt-bindings: media: Convert MediaTek mt8173-mdp
bindings to DT schema") renames mediatek-mdp.txt to
mediatek,mt8173-mdp.yaml as part of this dt-binding conversion, but misses
to adjust the file entry in MEDIATEK MDP DRIVER.

Adjust the file entry after the conversion.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Reviewed-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>