MAINTAINERS: add tools/virtio/ under virtio

This should help make sure patches go to the correct list.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

MAINTAINERS

@@ -8758,6 +8758,7 @@ M:	"Michael S. Tsirkin" <mst@redhat.com>
 L:	virtualization@lists.linux-foundation.org
 S:	Maintained
 F:	drivers/virtio/
+F:	tools/virtio/
 F:	drivers/net/virtio_net.c
 F:	drivers/block/virtio_blk.c
 F:	include/linux/virtio_*.h