MAINTAINERS: add files for Mediatek DRM drivers

Mediatek MIPI DSI phy driver is moved from drivers/gpu/drm/mediatek to
drivers/phy/mediatek, so add the new folder to the Mediatek DRM drivers'
information.

Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Acked-by: Chunfeng Yun <chunfeng.yun@mediatek.com>

MAINTAINERS

@@ -5867,6 +5867,7 @@ S:	Supported
 F:	Documentation/devicetree/bindings/display/mediatek/
 F:	drivers/gpu/drm/mediatek/
 F:	drivers/phy/mediatek/phy-mtk-hdmi*
+F:	drivers/phy/mediatek/phy-mtk-mipi*
 
 DRM DRIVERS FOR NVIDIA TEGRA
 M:	Thierry Reding <thierry.reding@gmail.com>