drm/omap: use drm_atomic_helper_shutdown()

Use drm_atomic_helper_shutdown() to ensure that all crtcs are disabled
when unloading the driver.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/gpu/drm/omapdrm/omap_drv.c

@@ -865,6 +865,8 @@ static int pdev_remove(struct platform_device *pdev)
 	if (priv->fbdev)
 		omap_fbdev_free(ddev);
 
+	drm_atomic_helper_shutdown(ddev);
+
 	drm_mode_config_cleanup(ddev);
 
 	omap_drm_irq_uninstall(ddev);