For non-mmio devices, should set fc values to proper txwi config

Fixes: 48fab5bb ("mt76: mt7921: introduce mt7921s support")
Tested-by: Sean Wang <sean.wang@mediatek.com>
Co-developed-by: Leon Yen <Leon.Yen@mediatek.com>
Signed-off-by: Leon Yen <Leon.Yen@mediatek.com>
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>