MAINTAINERS: add VFIO ISM PCI DRIVER section

ism_vfio_pci is a new kernel component that allows
to use the ISM device from userspace. Add myself
as a maintainer.

Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Julian Ruess <julianr@linux.ibm.com>
Link: https://lore.kernel.org/r/20260325-vfio_pci_ism-v8-3-ddc504cde914@linux.ibm.com
Signed-off-by: Alex Williamson <alex@shazbot.org>

Author: juru1234

MAINTAINERS

@@ -27710,6 +27710,12 @@ L:	kvm@vger.kernel.org
 S:	Maintained
 F:	drivers/vfio/pci/hisilicon/
 
+VFIO ISM PCI DRIVER
+M:	Julian Ruess <julianr@linux.ibm.com>
+L:	kvm@vger.kernel.org
+S:	Maintained
+F:	drivers/vfio/pci/ism/
+
 VFIO MEDIATED DEVICE DRIVERS
 M:	Kirti Wankhede <kwankhede@nvidia.com>
 L:	kvm@vger.kernel.org