MAINTAINERS: Saying goodbye to Hans J. Koch

We had to say goodbye when Hans passed away recently. Hans was a
free-software enthusiast and an active contributor. He was the main author
and maintainer of the UIO subsystem and contributed in various ways to the
Linux kernel as a professional and hobbyist. He is greatly missed.

Signed-off-by: Benedikt Spranger <b.spranger@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>