mt76: do not use devm API for led classdev

With the devm API, the unregister happens after the device cleanup is done,
after which the struct mt76_dev which contains the led_cdev has already been
freed. This leads to a use-after-free bug that can crash the system.
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mac80211.c

@@ -105,7 +105,15 @@ static int mt76_led_init(struct mt76_dev *dev)
 		dev->led_al = of_property_read_bool(np, "led-active-low");
 	}
 
-	return devm_led_classdev_register(dev->dev, &dev->led_cdev);
+	return led_classdev_register(dev->dev, &dev->led_cdev);
+}
+
+static void mt76_led_cleanup(struct mt76_dev *dev)
+{
+	if (!dev->led_cdev.brightness_set && !dev->led_cdev.blink_set)
+		return;
+
+	led_classdev_unregister(&dev->led_cdev);
 }
 
 static void mt76_init_stream_cap(struct mt76_dev *dev,
@@ -362,6 +370,7 @@ void mt76_unregister_device(struct mt76_dev *dev)
 {
 	struct ieee80211_hw *hw = dev->hw;
 
+	mt76_led_cleanup(dev);
 	mt76_tx_status_check(dev, NULL, true);
 	ieee80211_unregister_hw(hw);
 }