MAINTAINERS: Add myself as virtio-balloon co-maintainer

As suggested by Michael, let's add me as co-maintainer of virtio-balloon.
While at it, also add "include/linux/balloon_compaction.h" to the file
list.

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20200310115411.12760-1-david@redhat.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

MAINTAINERS

@@ -17909,9 +17909,18 @@ F:	drivers/virtio/
 F:	include/linux/vdpa.h
 F:	include/linux/virtio*.h
 F:	include/uapi/linux/virtio_*.h
-F:	mm/balloon_compaction.c
 F:	tools/virtio/
 
+VIRTIO BALLOON
+M:	"Michael S. Tsirkin" <mst@redhat.com>
+M:	David Hildenbrand <david@redhat.com>
+L:	virtualization@lists.linux-foundation.org
+S:	Maintained
+F:	drivers/virtio/virtio_balloon.c
+F:	include/uapi/linux/virtio_balloon.h
+F:	include/linux/balloon_compaction.h
+F:	mm/balloon_compaction.c
+
 VIRTIO CRYPTO DRIVER
 M:	Gonglei <arei.gonglei@huawei.com>
 L:	virtualization@lists.linux-foundation.org