MAINTAINERS: update s390 machine file patterns

Some files used by s390 KVM code were missing in MAINTAINERS. Add
them.
Reported-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NSascha Silbe <silbe@linux.vnet.ibm.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>

MAINTAINERS

@@ -669,6 +669,9 @@ F: hw/s390x/
 F: include/hw/s390x/
 F: pc-bios/s390-ccw/
 F: hw/watchdog/wdt_diag288.c
+F: include/hw/watchdog/wdt_diag288.h
+F: pc-bios/s390-ccw.img
+F: default-configs/s390x-softmmu.mak
 T: git git://github.com/cohuck/qemu.git s390-next
 T: git git://github.com/borntraeger/qemu.git s390-next