ath9k: fix software retry counter tracking

The recent tx path cleanups moved the software retry count tracking
from the ath_buf to the skb cb, however the actual counter update
referred to the wrong location, confusing block-ack window tracking.
Fix this by using the retries counter in the struct ath_frame_info.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -250,11 +250,11 @@ static void ath_tid_drain(struct ath_softc *sc, struct ath_txq *txq,
 static void ath_tx_set_retry(struct ath_softc *sc, struct ath_txq *txq,
 			     struct sk_buff *skb)
 {
-	struct ieee80211_tx_info *tx_info = IEEE80211_SKB_CB(skb);
+	struct ath_frame_info *fi = get_frame_info(skb);
 	struct ieee80211_hdr *hdr;
 
 	TX_STAT_INC(txq->axq_qnum, a_retries);
-	if (tx_info->control.rates[4].count++ > 0)
+	if (fi->retries++ > 0)
 		return;
 
 	hdr = (struct ieee80211_hdr *)skb->data;