mt76: mt7615: cleanup mcu tx queue in mt7615_dma_reset()

With this patch, mt7615_mac_reset_work() can recover system back.

Fixes: e637763b ("mt76: move mcu queues to mt76_dev q_mcu array")
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>