[S390] fill out file list in s390 MAINTAINERS entry

Noticed with scripts/get_maintainer.pl -f fs/partitions/ibm.c
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

MAINTAINERS

@@ -4836,6 +4836,9 @@ W:	http://www.ibm.com/developerworks/linux/linux390/
 S:	Supported
 F:	arch/s390/
 F:	drivers/s390/
+F:	fs/partitions/ibm.c
+F:	Documentation/s390/
+F:	Documentation/DocBook/s390*
 
 S390 NETWORK DRIVERS
 M:	Ursula Braun <ursula.braun@de.ibm.com>