[S390] Update maintainers file.

Use the new linux-s390@vger.kernel.org mailing list instead of
linux-390@vm.marist.edu.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

MAINTAINERS

@@ -2791,7 +2791,7 @@ M:	schwidefsky@de.ibm.com
 P:	Heiko Carstens
 M:	heiko.carstens@de.ibm.com
 M:	linux390@de.ibm.com
-L:	linux-390@vm.marist.edu
+L:	linux-s390@vger.kernel.org
 W:	http://www.ibm.com/developerworks/linux/linux390/
 S:	Supported
 
@@ -2799,7 +2799,7 @@ S390 NETWORK DRIVERS
 P:	Frank Pavlic
 M:	fpavlic@de.ibm.com
 M:	linux390@de.ibm.com
-L:	linux-390@vm.marist.edu
+L:	linux-s390@vger.kernel.org
 W:	http://www.ibm.com/developerworks/linux/linux390/
 S:	Supported
 
@@ -2807,7 +2807,7 @@ S390 ZFCP DRIVER
 P:	Swen Schillig
 M:	swen@vnet.ibm.com
 M:	linux390@de.ibm.com
-L:	linux-390@vm.marist.edu
+L:	linux-s390@vger.kernel.org
 W:	http://www.ibm.com/developerworks/linux/linux390/
 S:	Supported