drm/exynos: Clear drvdata after component unbind

When components are unbound, DRM driver is unregistered and freed,
so clear drvdata to avoid potential use-after-free issue in
suspend/resume paths.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_drv.c

@@ -430,6 +430,7 @@ static void exynos_drm_unbind(struct device *dev)
 
 	kfree(drm->dev_private);
 	drm->dev_private = NULL;
+	dev_set_drvdata(dev, NULL);
 
 	drm_dev_unref(drm);
 }