staging: vboxvideo: adapt to new TTM interface

Fixes interface changes done in the following commits:
drm/ttm: add operation ctx to ttm_bo_validate v2
drm/ttm: add context to driver move callback as well

I missed this driver because it is in the staging area.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>