Pass virtio_gpu_object down to virtio_gpu_cmd_transfer_to_host_2d and
virtio_gpu_cmd_transfer_to_host_3d functions, instead of passing just
the virtio resource handle.

This is needed to lookup the scatter list of the object, for dma sync.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Reviewed-by: NJiandi An <jiandi.an@amd.com>
Tested-by: NJiandi An <jiandi.an@amd.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20180920062924.6514-1-kraxel@redhat.com