drm/virtio: allocate some extra bufs

virtio-gpu guest driver appearently can run out of buffers.
allocate some extra buffers, as quick stopgap for 4.9.
analyzing root cause and fixing it properly is TBD.

Reported-by: Jiri Slaby <jslaby@suse.cz>
Tested-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/virtio/virtgpu_vq.c

@@ -75,7 +75,7 @@ void virtio_gpu_cursor_ack(struct virtqueue *vq)
 int virtio_gpu_alloc_vbufs(struct virtio_gpu_device *vgdev)
 {
 	struct virtio_gpu_vbuffer *vbuf;
-	int i, size, count = 0;
+	int i, size, count = 16;
 	void *ptr;
 
 	INIT_LIST_HEAD(&vgdev->free_vbufs);