wifi: mt76: mt7915: fix beamforming availability check

Without this patch, when ap sets the tx stream number to 2,
ap won't send any beamforming packet.

Fixes: f89f297a ("mt76: mt7915: fix txbf starec TLV issues")
Signed-off-by: MeiChia Chiu <meichia.chiu@mediatek.com>
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

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

@@ -1019,13 +1019,13 @@ mt7915_is_ebf_supported(struct mt7915_phy *phy, struct ieee80211_vif *vif,
 			struct ieee80211_sta *sta, bool bfee)
 {
 	struct mt7915_vif *mvif = (struct mt7915_vif *)vif->drv_priv;
-	int tx_ant = hweight8(phy->mt76->chainmask) - 1;
+	int sts = hweight16(phy->mt76->chainmask);
 
 	if (vif->type != NL80211_IFTYPE_STATION &&
 	    vif->type != NL80211_IFTYPE_AP)
 		return false;
 
-	if (!bfee && tx_ant < 2)
+	if (!bfee && sts < 2)
 		return false;
 
 	if (sta->deflink.he_cap.has_he) {