drm/gma500: Use backlight_get_brightness() to get the brightness

Use backlight_get_brightness() instead of directly referencing
bd->props.brightness. This will take backlight_is_blank() into account,
properly setting brightness to 0 when screen-blanking has been requested
through the backlight sysfs interface.
Suggested-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220917205920.647212-4-hdegoede@redhat.com

drivers/gpu/drm/gma500/backlight.c

@@ -52,7 +52,7 @@ static int gma_backlight_get_brightness(struct backlight_device *bd)
 static int gma_backlight_update_status(struct backlight_device *bd)
 {
 	struct drm_device *dev = bl_get_data(bd);
-	int level = bd->props.brightness;
+	int level = backlight_get_brightness(bd);
 
 	/* Percentage 1-100% being valid */
 	if (level < 1)