dell-laptop: fix to return error code in dell_send_intensity()

Fix to return error code instead always return 0 from function
dell_send_intensity().
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>

drivers/platform/x86/dell-laptop.c

@@ -684,7 +684,7 @@ static int dell_send_intensity(struct backlight_device *bd)
 
 out:
 	release_buffer();
-	return 0;
+	return ret;
 }
 
 static int dell_get_intensity(struct backlight_device *bd)