ath9k: make use of conf_is_ht*() in the rest of the driver

Use shiny new conf_is_ht*() helpers, we can later remove ht.enabled if
desired.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath9k/xmit.c b/drivers/net/wireless/ath9k/xmit.c
index e28889b..9e910f7 100644
--- a/drivers/net/wireless/ath9k/xmit.c
+++ b/drivers/net/wireless/ath9k/xmit.c
@@ -1690,7 +1690,7 @@
 	(sc->sc_flags & SC_OP_PREAMBLE_SHORT) ?
 		(bf->bf_state.bf_type |= BUF_SHORT_PREAMBLE) :
 		(bf->bf_state.bf_type &= ~BUF_SHORT_PREAMBLE);
-	(sc->hw->conf.ht.enabled && !is_pae(skb) &&
+	(conf_is_ht(&sc->hw->conf) && !is_pae(skb) &&
 	 (tx_info->flags & IEEE80211_TX_CTL_AMPDU)) ?
 		(bf->bf_state.bf_type |= BUF_HT) :
 		(bf->bf_state.bf_type &= ~BUF_HT);