backlight: arcxcnn: Use backlight helper

Instead of retrieving the backlight brightness in struct
backlight_properties manually, and then checking whether the backlight
should be on at all, use backlight_get_brightness() which does all
this and insulates this from future changes.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230106164856.1453819-3-steve@sk2.org

drivers/video/backlight/arcxcnn_bl.c

@@ -130,12 +130,9 @@ static int arcxcnn_set_brightness(struct arcxcnn *lp, u32 brightness)
 static int arcxcnn_bl_update_status(struct backlight_device *bl)
 {
 	struct arcxcnn *lp = bl_get_data(bl);
-	u32 brightness = bl->props.brightness;
+	u32 brightness = backlight_get_brightness(bl);
 	int ret;
 
-	if (bl->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK))
-		brightness = 0;
-
 	ret = arcxcnn_set_brightness(lp, brightness);
 	if (ret)
 		return ret;