MAINTAINERS: Add entry for ASPEED pinctrl drivers

Add myself as maintainer to avoid burdening others with the madness.

Cc: Johnny Huang <johnny_huang@aspeedtech.com>
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Link: https://lore.kernel.org/r/20190628023838.15426-5-andrew@aj.id.au


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>