wifi: mt76: mt7925e: fix use-after-free in free_irq()

From commit a304e1b8 ("[PATCH] Debug shared irqs"), there is a test
to make sure the shared irq handler should be able to handle the unexpected
event after deregistration. For this case, let's apply MT76_REMOVED flag to
indicate the device was removed and do not run into the resource access
anymore.

Fixes: c948b5da ("wifi: mt76: mt7925: add Mediatek Wi-Fi7 driver for mt7925 chips")
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>