MAINTAINERS: update files of MediaTek USB3 PHYs

Update maintained files include MediaTek USB3 PHYs drivers and
their bindings

Signed-off-by: Chunfeng Yun <[e-mail]>
Signed-off-by: Kishon Vijay Abraham I <[e-mail]>

MAINTAINERS

···
 L:	[e-mail] (moderated for non-subscribers)
 L:	[e-mail] (moderated for non-subscribers)
 S:	Maintained
-F:	drivers/phy/mediatek/phy-mtk-tphy.c
+F:	drivers/phy/mediatek/
+F:	Documentation/devicetree/bindings/phy/phy-mtk-*
 
 ARM/MICREL KS8695 ARCHITECTURE
 M:	Greg Ungerer <[e-mail]>