mt76x2: use mt76_dev instead of mt76x2_dev in mt76x2_tx_queue_mcu

Use mt76_dev data structure instead of mt76x2_dev one in
mt76x2_tx_queue_mcu routine. This is a preliminary patch
to share mcu code between mt76x2e and mt76x0e

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>