MAINTAINERS: move Jens Osterkamp to CREDITS

Jens' email address bounces, so move his name and entry to CREDITS.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Ishizaki Kou <kou.ishizaki@toshiba.co.jp>
Cc: Jens Osterkamp <jens@linux.vnet.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>