ax25: Replace kfree() in ax25_dev_free() with ax25_dev_put()

The object "ax25_dev" is managed by reference counting. Thus it should
not be directly released by kfree(), replace with ax25_dev_put().

Fixes: d01ffb9 ("ax25: add refcount in ax25_dev to avoid UAF bugs")
Suggested-by: Dan Carpenter <[email protected]>
Signed-off-by: Duoming Zhou <[email protected]>
Reviewed-by: Dan Carpenter <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

net/ax25/ax25_dev.c

@@ -196,7 +196,7 @@ void __exit ax25_dev_free(void)
  list_for_each_entry_safe(s, n, &ax25_dev_list, list) {
  netdev_put(s->dev, &s->dev_tracker);
  list_del(&s->list);
- kfree(s);
+ ax25_dev_put(s);
  }
  spin_unlock_bh(&ax25_dev_lock);
 }