minstrel_ht: fix check for downgrading of top2 rate

The check should be against current top2 rate, instead of
current top rate.
Signed-off-by: NMing Lei <tom.leiming@gmail.com>
Acked-by: NFelix Fietkau <nbd@openwrt.org>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

net/mac80211/rc80211_minstrel_ht.c

@@ -443,8 +443,8 @@ minstrel_ht_tx_status(void *priv, struct ieee80211_supported_band *sband,
 		minstrel_downgrade_rate(mi, &mi->max_tp_rate, true);
 
 	rate2 = minstrel_get_ratestats(mi, mi->max_tp_rate2);
-	if (rate->attempts > 30 &&
-	    MINSTREL_FRAC(rate->success, rate->attempts) <
+	if (rate2->attempts > 30 &&
+	    MINSTREL_FRAC(rate2->success, rate2->attempts) <
 	    MINSTREL_FRAC(20, 100))
 		minstrel_downgrade_rate(mi, &mi->max_tp_rate2, false);