Bluetooth: hci_sync: fix race in hci_cmd_sync_dequeue_once

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: hci_sync: fix race in hci_cmd_sync_dequeue_once hci_cmd_sync_dequeue_once() does lookup and then cancel the entry under two separate lock sections. Meanwhile, hci_cmd_sync_work() can also delete the same entry, leading to double list_del() and "UAF". Fix this by holding cmd_sync_work_lock across both lookup and cancel, so that the entry cannot be removed concurrently.