mt76: connac: fix up the setting for ht40 mode in mt76_connac_mcu_uni_add_bss

Use proper value for ht40 mode configuration in mt76_connac_mcu_uni_add_bss
routine and not ht20 one

Fixes: d0e274af

 ("mt76: mt76_connac: create mcu library")
Co-developed-by: Soul Huang <Soul.Huang@mediatek.com>
Signed-off-by: Soul Huang <Soul.Huang@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>