mt76: connac: fix last_chan configuration in mt76_connac_mcu_rate_txpower_band

last_ch configuration must not be dependent on the current configured band
but it is defined by hw capabilities since the fw always expects the
following order:
- 2GHz
- 5GHz
- 6GHz

Fixes: 9b2ea8ee ("mt76: connac: set 6G phymode in single-sku support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.c

@@ -1980,12 +1980,12 @@ mt76_connac_mcu_rate_txpower_band(struct mt76_phy *phy,
 	}
 	batch_size = DIV_ROUND_UP(n_chan, batch_len);
 
-	if (!phy->cap.has_5ghz)
-		last_ch = chan_list_2ghz[n_chan - 1];
-	else if (phy->cap.has_6ghz)
-		last_ch = chan_list_6ghz[n_chan - 1];
+	if (phy->cap.has_6ghz)
+		last_ch = chan_list_6ghz[ARRAY_SIZE(chan_list_6ghz) - 1];
+	else if (phy->cap.has_5ghz)
+		last_ch = chan_list_5ghz[ARRAY_SIZE(chan_list_5ghz) - 1];
 	else
-		last_ch = chan_list_5ghz[n_chan - 1];
+		last_ch = chan_list_2ghz[ARRAY_SIZE(chan_list_2ghz) - 1];
 
 	for (i = 0; i < batch_size; i++) {
 		struct mt76_connac_tx_power_limit_tlv tx_power_tlv = {};