mt76: mt7921: fix crash when startup fails.

If the nic fails to start, it is possible that the
reset_work has already been scheduled.  Ensure the
work item is canceled so we do not have use-after-free
crash in case cleanup is called before the work item
is executed.

This fixes crash on my x86_64 apu2 when mt7921k radio
fails to work.  Radio still fails, but OS does not
crash.
Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7921/main.c

@@ -273,6 +273,7 @@ static void mt7921_stop(struct ieee80211_hw *hw)
 
 	cancel_delayed_work_sync(&dev->pm.ps_work);
 	cancel_work_sync(&dev->pm.wake_work);
+	cancel_work_sync(&dev->reset_work);
 	mt76_connac_free_pending_tx_skbs(&dev->pm, NULL);
 
 	mt7921_mutex_acquire(dev);