drm/mediatek: don't use drm_put_dev

fsl is already fully demidlayered in the probe function, but for
convenience stuck with drm_put_dev. Call the unregister/unref parts
separately, to make sure this driver works correct.

Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: CK Hu <ck.hu@mediatek.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161208110739.24417-3-daniel.vetter@ffwll.ch

drivers/gpu/drm/mediatek/mtk_drm_drv.c

@@ -321,7 +321,8 @@ static void mtk_drm_unbind(struct device *dev)
 {
 	struct mtk_drm_private *private = dev_get_drvdata(dev);
 
-	drm_put_dev(private->drm);
+	drm_dev_unregister(private->drm);
+	drm_dev_unref(private->drm);
 	private->drm = NULL;
 }