ath9k: initialize tx chainmask before testing channel tx power values

With an uninitialized chainmask, the per-channel power will only contain
the power limits for a single chain instead of the combined tx power.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Cc: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/init.c

@@ -669,8 +669,10 @@ static void ath9k_init_band_txpower(struct ath_softc *sc, int band)
 static void ath9k_init_txpower_limits(struct ath_softc *sc)
 {
 	struct ath_hw *ah = sc->sc_ah;
+	struct ath_common *common = ath9k_hw_common(sc->sc_ah);
 	struct ath9k_channel *curchan = ah->curchan;
 
+	ah->txchainmask = common->tx_chainmask;
 	if (ah->caps.hw_caps & ATH9K_HW_CAP_2GHZ)
 		ath9k_init_band_txpower(sc, IEEE80211_BAND_2GHZ);
 	if (ah->caps.hw_caps & ATH9K_HW_CAP_5GHZ)