mt76: mt7915: fix ht mcs in mt7915_mac_add_txs_skb()

The mcs value of HT mode reported by mt7915_mac_add_txs_skb()
has already been converted to the expected format.

Fixes: 9908d98a ("mt76: mt7915: report tx rate directly from tx status")
Signed-off-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7915/mac.c

@@ -1568,7 +1568,6 @@ mt7915_mac_add_txs_skb(struct mt7915_dev *dev, struct mt76_wcid *wcid, int pid,
 		break;
 	case MT_PHY_TYPE_HT:
 	case MT_PHY_TYPE_HT_GF:
-		rate.mcs += (rate.nss - 1) * 8;
 		if (rate.mcs > 31)
 			goto out;