MAINTAINERS: friendly takeover of i2c-gpio driver

I haven't heard from Haavard in years despite putting him to the CC list for
i2c-gpio related mails. Since I was doing the work on this driver for a while
now, let me take official maintainership, so it will be more clear to users.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Haavard Skinnemoen <hskinnemoen@gmail.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>