qcacmn: Fix avg_tx_rate computaion

Assign dp_ath_rate_lpf return value to avg_tx_rate,
which is further used to compute ppdu_tx_rate

Change-Id: Ib51be85c2436bef8feffeb611982314720399a69
CRs-Fixed: 2356831

dp/wifi3.0/dp_htt.c

@@ -114,7 +114,8 @@ dp_tx_rate_stats_update(struct dp_peer *peer,
 	if (!ratekbps)
 		return;
 
-	dp_ath_rate_lpf(peer->stats.tx.avg_tx_rate, ratekbps);
+	peer->stats.tx.avg_tx_rate =
+		dp_ath_rate_lpf(peer->stats.tx.avg_tx_rate, ratekbps);
 	ppdu_tx_rate = dp_ath_rate_out(peer->stats.tx.avg_tx_rate);
 	DP_STATS_UPD(peer, tx.rnd_avg_tx_rate, ppdu_tx_rate);