ath9k: use the right hw on ath_tx_setup_buffer() for HT

When using virtual wiphys the base sc->hw was being used, the correct
hw is passed along the caller already so just use that.

Cc: Jouni.Malinen <Jouni.Malinen@atheros.com>
Signed-off-by: NLuis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

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

@@ -1576,7 +1576,7 @@ static int ath_tx_setup_buffer(struct ieee80211_hw *hw, struct ath_buf *bf,
 
 	bf->bf_frmlen = skb->len + FCS_LEN - (hdrlen & 3);
 
-	if (conf_is_ht(&sc->hw->conf) && !is_pae(skb))
+	if (conf_is_ht(&hw->conf) && !is_pae(skb))
 		bf->bf_state.bf_type |= BUF_HT;
 
 	bf->bf_flags = setup_tx_flags(sc, skb, txctl->txq);