mt76: use cancel_delayed_work_sync in mt76_rx_aggr_shutdown

The workqueue item needs to be fully shut down before the struct can be
freed.
Signed-off-by: NFelix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/agg-rx.c

@@ -257,7 +257,7 @@ static void mt76_rx_aggr_shutdown(struct mt76_dev *dev, struct mt76_rx_tid *tid)
 	u8 size = tid->size;
 	int i;
 
-	cancel_delayed_work(&tid->reorder_work);
+	cancel_delayed_work_sync(&tid->reorder_work);
 
 	spin_lock_bh(&tid->lock);