wifi: mt76: mt7915: fix tlv length of mt7915_mcu_get_chan_mib_info

Correct per-device TLV lengths to avoid invalid operation in firmware.
(  64.040375:28:STATS-E)statsGetSingleHWCounter: MIB counter index = 65472 not supported.
This happens on mt7916/mt7986.

Fixes: b0bfa005 ("wifi: mt76: mt7915: improve accuracy of time_busy calculation")
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7915/mcu.c

@@ -3038,7 +3038,7 @@ int mt7915_mcu_get_chan_mib_info(struct mt7915_phy *phy, bool chan_switch)
 	}
 
 	ret = mt76_mcu_send_and_get_msg(&dev->mt76, MCU_EXT_CMD(GET_MIB_INFO),
-					req, sizeof(req), true, &skb);
+					req, len * sizeof(req[0]), true, &skb);
 	if (ret)
 		return ret;