drm: shmobile: Use backlight helper

This started with work on the removal of backlight_properties'
deprecated fb_blank field, much of which can be taken care of by using
helper functions provided by backlight.h instead of directly accessing
fields in backlight_properties. This patch series doesn't involve
fb_blank, but it still seems useful to use helper functions where
appropriate.

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: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220616170821.1348169-1-steve@sk2.org

drivers/gpu/drm/shmobile/shmob_drm_backlight.c

@@ -18,11 +18,7 @@ static int shmob_drm_backlight_update(struct backlight_device *bdev)
 	struct shmob_drm_connector *scon = bl_get_data(bdev);
 	struct shmob_drm_device *sdev = scon->connector.dev->dev_private;
 	const struct shmob_drm_backlight_data *bdata = &sdev->pdata->backlight;
-	int brightness = bdev->props.brightness;
-
-	if (bdev->props.power != FB_BLANK_UNBLANK ||
-	    bdev->props.state & BL_CORE_SUSPENDED)
-		brightness = 0;
+	int brightness = backlight_get_brightness(bdev);
 
 	return bdata->set_brightness(brightness);
 }