ath9k: Fix regression in 'xmit' debugfs file

Commit "ath9k: Fix the 'xmit' debugfs file" changed the
the array size of ath_stats.txstats to IEEE80211_NUM_ACS,
which is wrong because the HW queue number is used to
update the statistics. Revert back to using ATH9K_NUM_TX_QUEUES.
Reported-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/debug.h

@@ -242,7 +242,7 @@ struct ath_rx_stats {
 
 struct ath_stats {
 	struct ath_interrupt_stats istats;
-	struct ath_tx_stats txstats[IEEE80211_NUM_ACS];
+	struct ath_tx_stats txstats[ATH9K_NUM_TX_QUEUES];
 	struct ath_rx_stats rxstats;
 	struct ath_dfs_stats dfs_stats;
 	u32 reset[__RESET_TYPE_MAX];