mt76: mt7615: parse mcu return code for unified commands

Add return code parsing for the following unified commands:
- MCU_UNI_CMD_DEV_INFO_UPDATE
- MCU_UNI_CMD_BSS_INFO_UPDATE
- MCU_UNI_CMD_STA_REC_UPDATE

Co-developed-by: Sean Wang <sean.wang@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>