drm/omap: Make the video_mode pointer to .set_timings() const

The .set_timings() operations of the omap_dss_device instances don't
need to modify the passed timings. Make the pointer const.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/gpu/drm/omapdrm/dss/hdmi5.c

@@ -262,7 +262,7 @@ static int hdmi_display_check_timings(struct omap_dss_device *dssdev,
 }
 
 static void hdmi_display_set_timings(struct omap_dss_device *dssdev,
-				     struct videomode *vm)
+				     const struct videomode *vm)
 {
 	struct omap_hdmi *hdmi = dssdev_to_hdmi(dssdev);