mt76x02: fix hdr pointer in write txwi for USB

Since we add txwi at the begining of skb->data, it no longer point
to ieee80211_hdr. This breaks settings TS bit for probe response and
beacons.
Acked-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt76x02_usb_core.c

@@ -85,8 +85,9 @@ int mt76x02u_tx_prepare_skb(struct mt76_dev *mdev, void *data,
 
 	mt76x02_insert_hdr_pad(skb);
 
-	txwi = skb_push(skb, sizeof(struct mt76x02_txwi));
+	txwi = (struct mt76x02_txwi *)(skb->data - sizeof(struct mt76x02_txwi));
 	mt76x02_mac_write_txwi(dev, txwi, skb, wcid, sta, len);
+	skb_push(skb, sizeof(struct mt76x02_txwi));
 
 	pid = mt76_tx_status_skb_add(mdev, wcid, skb);
 	txwi->pktid = pid;