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 <[e-mail]>
Reviewed-by: Sam Ravnborg <[e-mail]>
Reviewed-by: Daniel Thompson <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/video/backlight/arcxcnn_bl.c

···
 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)