MAINTAINERS: add Karsten as SMC maintainer

Add Karsten as additional maintainer for Shared Memory Communications
(SMC) Sockets.
Acked-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

MAINTAINERS

@@ -13760,6 +13760,7 @@ F:	drivers/misc/sgi-xp/
 
 SHARED MEMORY COMMUNICATIONS (SMC) SOCKETS
 M:	Ursula Braun <ubraun@linux.ibm.com>
+M:	Karsten Graul <kgraul@linux.ibm.com>
 L:	linux-s390@vger.kernel.org
 W:	http://www.ibm.com/developerworks/linux/linux390/
 S:	Supported