MAINTAINERS: Change maintainer for gpio-bcm-kona.c

Since I no longer have access to the hardware, Ray Jui will take over
maintaining the Kona GPIO driver.

In addition, my former e-mail addresses mmayer@broadcom.com and
markus.mayer@linaro.org will cease to function shortly. So, I used an
address I can still be reached at as the "author" addess here.

Signed-off-by: Markus Mayer <code@mmayer.net>
Signed-off-by: Markus Mayer <markus.mayer@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>