pinctrl: mediatek: update MAINTAINERS entry with MediaTek pinctrl driver

pinctrl: mediatek: update MAINTAINERS entry with MediaTek pinctrl driver

I work for MediaTek on maintaining the existing MediaTek SoC whose target
to home gateway such as MT7622 and MT7623 that is reusing MT2701 related
files and will keep adding support for the following such kinds of SoCs
in the future.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Reviewed-by: Biao Huang <biao.huang@mediatek.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>