MAINTAINERS: Add myself as virtio-mem maintainer

Let's make sure patches/bug reports find the right person.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20200507140139.17083-3-david@redhat.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

MAINTAINERS

@@ -17986,6 +17986,13 @@ S:	Maintained
 F:	drivers/iommu/virtio-iommu.c
 F:	include/uapi/linux/virtio_iommu.h
 
+VIRTIO MEM DRIVER
+M:	David Hildenbrand <david@redhat.com>
+L:	virtualization@lists.linux-foundation.org
+S:	Maintained
+F:	drivers/virtio/virtio_mem.c
+F:	include/uapi/linux/virtio_mem.h
+
 VIRTUAL BOX GUEST DEVICE DRIVER
 M:	Hans de Goede <hdegoede@redhat.com>
 M:	Arnd Bergmann <arnd@arndb.de>