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 <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Reviewed-by: Jyri Sarha <[e-mail]>
Acked-by: Sam Ravnborg <[e-mail]>

drivers/gpu/drm/tilcdc/tilcdc_panel.c

···
 		{ },
 };
 
-struct platform_driver panel_driver = {
+static struct platform_driver panel_driver = {
 	.probe = panel_probe,
 	.remove = panel_remove,
 	.driver = {