virtio_balloon: fix sparse warning

balloon uses virtio32_to_cpu instead of cpu_to_virtio32
to convert a native endian number to virtio.
No practical difference but makes sparse warn.
Fix it up.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>

drivers/virtio/virtio_balloon.c

@@ -600,7 +600,7 @@ static int send_cmd_id_start(struct virtio_balloon *vb)
 	while (virtqueue_get_buf(vq, &unused))
 		;
 
-	vb->cmd_id_active = virtio32_to_cpu(vb->vdev,
+	vb->cmd_id_active = cpu_to_virtio32(vb->vdev,
 					virtio_balloon_cmd_id_received(vb));
 	sg_init_one(&sg, &vb->cmd_id_active, sizeof(vb->cmd_id_active));
 	err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_active, GFP_KERNEL);