virtio-mmio: update queue size on guest write

Some guests read back queue size after writing it.
Always update the on size write otherwise they might be confused.

Cc: qemu-stable@nongnu.org
Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
Message-Id: <20191224081446.17003-1-dplotnikov@virtuozzo.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio-mmio.c

@@ -308,8 +308,9 @@ static void virtio_mmio_write(void *opaque, hwaddr offset, uint64_t value,
         break;
     case VIRTIO_MMIO_QUEUE_NUM:
         trace_virtio_mmio_queue_write(value, VIRTQUEUE_MAX_SIZE);
+        virtio_queue_set_num(vdev, vdev->queue_sel, value);
+
         if (proxy->legacy) {
-            virtio_queue_set_num(vdev, vdev->queue_sel, value);
             virtio_queue_update_rings(vdev, vdev->queue_sel);
         } else {
             proxy->vqs[vdev->queue_sel].num = value;