wifi: rtw89: fw: scan offload prohibit all 6 GHz channel if no 6 GHz sband

We have some policy via BIOS to block uses of 6 GHz. In this case, 6 GHz
sband will be NULL even if it is WiFi 7 chip. So, add NULL handling here
to avoid crash.
Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://msgid.link/20240412115729.8316-3-pkshih@realtek.com

drivers/net/wireless/realtek/rtw89/fw.c

@@ -4689,6 +4689,10 @@ static void rtw89_scan_get_6g_disabled_chan(struct rtw89_dev *rtwdev,
 	u8 i, idx;
 
 	sband = rtwdev->hw->wiphy->bands[NL80211_BAND_6GHZ];
+	if (!sband) {
+		option->prohib_chan = U64_MAX;
+		return;
+	}
 
 	for (i = 0; i < sband->n_channels; i++) {
 		chan = &sband->channels[i];