MAINTAINERS: change mail adress of Hans J. Koch

My old mail address doesn't exist anymore.  This patch changes all
occurences in MAINTAINERS to my new address.

Signed-off-by: Hans J. Koch <hjk@hansjkoch.de>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>