drm/tilcdc: Use backlight power constants

Replace FB_BLANK_ constants with their counterparts from the
backlight subsystem. The values are identical, so there's no
change in functionality or semantics.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Jyri Sarha <jyri.sarha@iki.fi>
Cc: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240731122311.1143153-10-tzimmermann@suse.de

drivers/gpu/drm/tilcdc/tilcdc_panel.c

@@ -49,7 +49,7 @@ static void panel_encoder_dpms(struct drm_encoder *encoder, int mode)
 
 	if (backlight) {
 		backlight->props.power = mode == DRM_MODE_DPMS_ON ?
-					 FB_BLANK_UNBLANK : FB_BLANK_POWERDOWN;
+					 BACKLIGHT_POWER_ON : BACKLIGHT_POWER_OFF;
 		backlight_update_status(backlight);
 	}