mt76: mt7603: fix tx status HT rate validation

Use the correct variable in the check. Fixes an uninitialized variable warning

Reported-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Fixes: c8846e1015022 ("mt76: add driver for MT7603E and MT7628/7688")
Signed-off-by: Felix Fietkau <nbd@nbd.name>

mt7603/mac.c

@@ -1072,7 +1072,7 @@ mt7603_fill_txs(struct mt7603_dev *dev, struct mt7603_sta *sta,
 	case MT_PHY_TYPE_HT:
 		final_rate_flags |= IEEE80211_TX_RC_MCS;
 		final_rate &= GENMASK(5, 0);
-		if (i > 15)
+		if (final_rate > 15)
 			return false;
 		break;
 	default: