I didn't find any user of the driver data yet, so store the
drm_device pointer in there.

Cc: Inki Dae <inki.dae@samsung.com>
Acked-by: NInki Dae <inki.dae@samsung.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: NDave Airlie <airlied@redhat.com>