virtio-balloon: Constify id_table

id_table is not modified, so make it const to allow the compiler to put
it in read-only memory.
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Link: https://lore.kernel.org/r/20200911203509.26505-2-rikard.falkeborn@gmail.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>

drivers/virtio/virtio_balloon.c

@@ -128,7 +128,7 @@ struct virtio_balloon {
 	struct page_reporting_dev_info pr_dev_info;
 };
 
-static struct virtio_device_id id_table[] = {
+static const struct virtio_device_id id_table[] = {
 	{ VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
 	{ 0 },
 };