wifi: mt76: mt7921: fix potential deadlock in mt7921_roc_abort_sync

wifi: mt76: mt7921: fix potential deadlock in mt7921_roc_abort_sync

roc_abort_sync() can deadlock with roc_work(). roc_work() holds
dev->mt76.mutex, while cancel_work_sync() waits for roc_work()
to finish. If the caller already owns the same mutex, both
sides block and no progress is possible.

This deadlock can occur during station removal when
mt76_sta_state() -> mt76_sta_remove() -> mt7921_mac_sta_remove() ->
mt7921_roc_abort_sync() invokes cancel_work_sync() while
roc_work() is still running and holding dev->mt76.mutex.

This avoids the mutex deadlock and preserves exactly-once
work ownership.

Fixes: 352d966126e6 ("wifi: mt76: mt7921: fix a potential association failure upon resuming")
Co-developed-by: Quan Zhou <quan.zhou@mediatek.com>
Signed-off-by: Quan Zhou <quan.zhou@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Link: https://patch.msgid.link/20260126180013.8167-1-sean.wang@kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>