wcn36xx: Fix warning due to bad rate_idx

The rate_idx is the index of the bitrate in the supported rate table.
However the 5Ghz band has a smaller legacy bitrate table than 2.4Ghz
since it does not have the DSSS bitrates (1, 2, 5.5, 11).

So in 5Ghz band the index should adjusted accrodingly (-4).
Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
[bod: Made sure fix is only applied if the rate_idx > n_bitrates]
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200829033846.2167619-6-bryan.odonoghue@linaro.org

drivers/net/wireless/ath/wcn36xx/txrx.c

@@ -230,6 +230,7 @@ int wcn36xx_rx_skb(struct wcn36xx *wcn, struct sk_buff *skb)
 	const struct wcn36xx_rate *rate;
 	struct ieee80211_hdr *hdr;
 	struct wcn36xx_rx_bd *bd;
+	struct ieee80211_supported_band *sband;
 	u16 fc, sn;
 
 	/*
@@ -270,6 +271,14 @@ int wcn36xx_rx_skb(struct wcn36xx *wcn, struct sk_buff *skb)
 		status.enc_flags = rate->encoding_flags;
 		status.bw = rate->bw;
 		status.rate_idx = rate->mcs_or_legacy_index;
+		sband = wcn->hw->wiphy->bands[status.band];
+
+		if (status.band == NL80211_BAND_5GHZ &&
+		    status.encoding == RX_ENC_LEGACY &&
+		    status.rate_idx >= sband->n_bitrates) {
+			/* no dsss rates in 5Ghz rates table */
+			status.rate_idx -= 4;
+		}
 	} else {
 		status.encoding = 0;
 		status.bw = 0;