mt76: mt7615: fix tx skb dma unmap

The first pointer in the txp needs to be unmapped as well, otherwise it will
leak DMA mapping entries

Fixes: 27d5c528 ("mt76: fix double DMA unmap of the first buffer on 7615/7915")
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7615/mac.c

@@ -690,7 +690,7 @@ mt7615_txp_skb_unmap_fw(struct mt76_dev *dev, struct mt7615_fw_txp *txp)
 {
 	int i;
 
-	for (i = 1; i < txp->nbuf; i++)
+	for (i = 0; i < txp->nbuf; i++)
 		dma_unmap_single(dev->dev, le32_to_cpu(txp->buf[i]),
 				 le16_to_cpu(txp->len[i]), DMA_TO_DEVICE);
 }