drm/tilcdc: add missing static for panel_driver

struct platform_driver panel_driver is only used from tilcdc_panel.c, so
it can be static.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200429104234.18910-3-tomi.valkeinen@ti.comReviewed-by: Jyri Sarha <jsarha@ti.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>

drivers/gpu/drm/tilcdc/tilcdc_panel.c

@@ -395,7 +395,7 @@ static const struct of_device_id panel_of_match[] = {
 		{ },
 };
 
-struct platform_driver panel_driver = {
+static struct platform_driver panel_driver = {
 	.probe = panel_probe,
 	.remove = panel_remove,
 	.driver = {