wifi: brcmfmac: avoid NULL-deref in survey dump for 2G only device

When dealing with a device for 2GHz band only the wiphy->bands for
5GHz will be NULL. This would result in a NULL-deref in the
brcmf_cfg80211_dump_survey() function. Rework the code with a
for-loop to make it easier to add another band.

Fixes: 6c04deae ("brcmfmac: Add dump_survey cfg80211 ops for HostApd AutoChannelSelection")
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230103124117.271988-3-arend.vanspriel@broadcom.com

drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c

@@ -7964,6 +7964,7 @@ brcmf_cfg80211_dump_survey(struct wiphy *wiphy, struct net_device *ndev,
 	struct brcmf_if *ifp = netdev_priv(cfg_to_ndev(cfg));
 	struct brcmf_dump_survey survey = {};
 	struct ieee80211_supported_band *band;
+	enum nl80211_band band_id;
 	struct cca_msrmnt_query req;
 	u32 noise;
 	int err;
@@ -7976,21 +7977,23 @@ brcmf_cfg80211_dump_survey(struct wiphy *wiphy, struct net_device *ndev,
 		return -EBUSY;
 	}
 
-	band = wiphy->bands[NL80211_BAND_2GHZ];
-	if (band && idx >= band->n_channels) {
+	for (band_id = 0; band_id < NUM_NL80211_BANDS; band_id++) {
+		band = wiphy->bands[band_id];
+		if (!band)
+			continue;
+		if (idx >= band->n_channels) {
 			idx -= band->n_channels;
-		band = NULL;
+			continue;
 		}
 
-	if (!band || idx >= band->n_channels) {
-		band = wiphy->bands[NL80211_BAND_5GHZ];
-		if (idx >= band->n_channels)
-			return -ENOENT;
+		info->channel = &band->channels[idx];
+		break;
 	}
+	if (band_id == NUM_NL80211_BANDS)
+		return -ENOENT;
 
 	/* Setting current channel to the requested channel */
 	info->filled = 0;
-	info->channel = &band->channels[idx];
 	if (cfg80211_set_channel(wiphy, ndev, info->channel, NL80211_CHAN_HT20))
 		return 0;