backlight: aat2870: 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: Daniel Thompson <[e-mail]>
Reviewed-by: Sam Ravnborg <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/video/backlight/aat2870_bl.c

···
 	struct aat2870_bl_driver_data *aat2870_bl = bl_get_data(bd);
 	struct aat2870_data *aat2870 =
 			dev_get_drvdata(aat2870_bl->pdev->dev.parent);
-	int brightness = bd->props.brightness;
+	int brightness = backlight_get_brightness(bd);
 	int ret;
 
 	if ((brightness < 0) || (bd->props.max_brightness < brightness)) {
···
 
 	dev_dbg(&bd->dev, "brightness=%d, power=%d, state=%d\n",
 		 bd->props.brightness, bd->props.power, bd->props.state);
-
-	if ((bd->props.power != FB_BLANK_UNBLANK) ||
-			(bd->props.state & BL_CORE_FBBLANK) ||
-			(bd->props.state & BL_CORE_SUSPENDED))
-		brightness = 0;
 
 	ret = aat2870->write(aat2870, AAT2870_BLM,
 			     (u8)aat2870_brightness(aat2870_bl, brightness));