wifi: mt76: mt7615: drop TXRX_NOTIFY on non-mmio buses

In the Linux kernel, the following vulnerability has been resolved: wifi: mt76: mt7615: drop TXRX_NOTIFY on non-mmio buses PKT_TYPE_TXRX_NOTIFY is an mmio-only event, but mt7615_rx_check() and mt7615_queue_rx_skb() dispatch it to mt7615_mac_tx_free() on every bus. mt7615_mac_tx_free() cleans the DMA tx queues with mt76_queue_tx_cleanup(), which calls queue_ops->tx_cleanup(). Only the mmio queue ops implement that callback; on the mt7663 USB and SDIO buses it is NULL, so a TXRX_NOTIFY there calls a NULL pointer in the RX worker. Same defect as the mt7921 and mt7925 patches in this series. Drop the event on non-mmio buses via mt76_is_mmio(), as in commit 5683e1488aa9 ("wifi: mt76: connac: do not check WED status for non-mmio devices").