MAINTAINERS: Remove Andy from GPIO maintainers

Too many things are going on, and reviewing GPIO related code
seems not the best I can do, hence I step down as a reviewer of
the GPIO subsystem.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>