fbdev: mx3fb: 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: Helge Deller <deller@gmx.de>
Cc: linux-fbdev@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Helge Deller <deller@gmx.de>

drivers/video/fbdev/mx3fb.c

@@ -283,12 +283,7 @@ static int mx3fb_bl_get_brightness(struct backlight_device *bl)
 static int mx3fb_bl_update_status(struct backlight_device *bl)
 {
 	struct mx3fb_data *fbd = bl_get_data(bl);
-	int brightness = bl->props.brightness;
-
-	if (bl->props.power != FB_BLANK_UNBLANK)
-		brightness = 0;
-	if (bl->props.fb_blank != FB_BLANK_UNBLANK)
-		brightness = 0;
+	int brightness = backlight_get_brightness(bl);
 
 	fbd->backlight_level = (fbd->backlight_level & ~0xFF) | brightness;