ieee802154: add myself as co-maintainer to MAINTAINERS file

Going to help Alexander, spread the review and development load.

Signed-off-by: Stefan Schmidt <stefan@osg.samsung.com>
Acked-by: Alexander Aring <aar@pengutronix.de>

MAINTAINERS

@@ -6105,6 +6105,7 @@ F:	drivers/idle/i7300_idle.c
 
 IEEE 802.15.4 SUBSYSTEM
 M:	Alexander Aring <aar@pengutronix.de>
+M:	Stefan Schmidt <stefan@osg.samsung.com>
 L:	linux-wpan@vger.kernel.org
 W:	http://wpan.cakelab.org/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth.git