ath9k: Fix multi-VIF BSS handling

mac80211 provides short preamble information and ERP protection
information on a per-BSS basis, which can be used. Remove flags
stored in the driver, which was incorrect since they were being used
in a global manner.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c
index d2c635d..5faec1e 100644
--- a/drivers/net/wireless/ath/ath9k/xmit.c
+++ b/drivers/net/wireless/ath/ath9k/xmit.c
@@ -955,7 +955,9 @@
 	 */
 	rate = ieee80211_get_rts_cts_rate(sc->hw, tx_info);
 	info->rtscts_rate = rate->hw_value;
-	if (sc->sc_flags & SC_OP_PREAMBLE_SHORT)
+
+	if (tx_info->control.vif &&
+	    tx_info->control.vif->bss_conf.use_short_preamble)
 		info->rtscts_rate |= rate->hw_value_short;
 
 	for (i = 0; i < 4; i++) {