platform/x86: acer-wmi: 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>
Cc: "Lee, Chun-Yi" <jlee@suse.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Mark Gross <markgross@kernel.org>
Cc: platform-driver-x86@vger.kernel.org
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20220607184635.1127913-2-steve@sk2.orgReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/acer-wmi.c

@@ -1615,12 +1615,7 @@ static int read_brightness(struct backlight_device *bd)
 
 static int update_bl_status(struct backlight_device *bd)
 {
-	int intensity = bd->props.brightness;
-
-	if (bd->props.power != FB_BLANK_UNBLANK)
-		intensity = 0;
-	if (bd->props.fb_blank != FB_BLANK_UNBLANK)
-		intensity = 0;
+	int intensity = backlight_get_brightness(bd);
 
 	set_u32(intensity, ACER_CAP_BRIGHTNESS);