staging: olpc_dcon: 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.

Cc: Jens Frederich <jfrederich@gmail.com>
Cc: Jon Nettleton <jon.nettleton@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-staging@lists.linux.dev
Signed-off-by: Stephen Kitt <steve@sk2.org>
Link: https://lore.kernel.org/r/20220607190049.1132154-1-steve@sk2.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/olpc_dcon/olpc_dcon.c

@@ -517,10 +517,7 @@ static struct device_attribute dcon_device_files[] = {
 static int dcon_bl_update(struct backlight_device *dev)
 {
 	struct dcon_priv *dcon = bl_get_data(dev);
-	u8 level = dev->props.brightness & 0x0F;
-
-	if (dev->props.power != FB_BLANK_UNBLANK)
-		level = 0;
+	u8 level = backlight_get_brightness(dev) & 0x0F;
 
 	if (level != dcon->bl_val)
 		dcon_set_backlight(dcon, level);