drm/exynos: dsi: remove the empty mode_valid callback

Because the helper function which calls this callback checks whether
it is registered or not. It is not necessary if it does nothing.
So it would be better to remove the function for clarity.

Signed-off-by: Hyungwon Hwang <human.hwang@samsung.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_dsi.c

@@ -1473,12 +1473,6 @@ static int exynos_dsi_get_modes(struct drm_connector *connector)
 	return 0;
 }
 
-static int exynos_dsi_mode_valid(struct drm_connector *connector,
-				 struct drm_display_mode *mode)
-{
-	return MODE_OK;
-}
-
 static struct drm_encoder *
 exynos_dsi_best_encoder(struct drm_connector *connector)
 {
@@ -1489,7 +1483,6 @@ exynos_dsi_best_encoder(struct drm_connector *connector)
 
 static struct drm_connector_helper_funcs exynos_dsi_connector_helper_funcs = {
 	.get_modes = exynos_dsi_get_modes,
-	.mode_valid = exynos_dsi_mode_valid,
 	.best_encoder = exynos_dsi_best_encoder,
 };