MAINTAINERS: add Matthew for s390 IOMMU

Acked-By: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

MAINTAINERS

@@ -14862,6 +14862,7 @@ F:	drivers/s390/block/dasd*
 F:	include/linux/dasd_mod.h
 
 S390 IOMMU (PCI)
+M:	Matthew Rosato <mjrosato@linux.ibm.com>
 M:	Gerald Schaefer <gerald.schaefer@linux.ibm.com>
 L:	linux-s390@vger.kernel.org
 S:	Supported