wifi: mt76: mt7925: fix incorrect length field in txpower command

commit ccb1863 upstream.

Set `tx_power_tlv->len` to `msg_len` instead of `sizeof(*tx_power_tlv)`
to ensure the correct message length is sent to firmware.

Cc: stable@vger.kernel.org
Fixes: c948b5d ("wifi: mt76: mt7925: add Mediatek Wi-Fi7 driver for mt7925 chips")
Signed-off-by: Ming Yen Hsieh <mingyen.hsieh@mediatek.com>
Link: https://patch.msgid.link/20250908072526.1833938-1-mingyen.hsieh@mediatek.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Ming Yen Hsieh

drivers/net/wireless/mediatek/mt76/mt7925/mcu.c

@@ -3673,7 +3673,7 @@ mt7925_mcu_rate_txpower_band(struct mt76_phy *phy,
 		memcpy(tx_power_tlv->alpha2, dev->alpha2, sizeof(dev->alpha2));
 		tx_power_tlv->n_chan = num_ch;
 		tx_power_tlv->tag = cpu_to_le16(0x1);
-		tx_power_tlv->len = cpu_to_le16(sizeof(*tx_power_tlv));
+		tx_power_tlv->len = cpu_to_le16(msg_len);
 
 		switch (band) {
 		case NL80211_BAND_2GHZ: