Bluetooth: hci_core: fix error handling in hci_register_dev()

If hci_register_suspend_notifier() returns error, the hdev and rfkill
are leaked. We could disregard the error and print a warning message
instead to avoid leaks, as it just means we won't be handing suspend
requests.

Fixes: 9952d90e

 ("Bluetooth: Handle PM_SUSPEND_PREPARE and PM_POST_SUSPEND")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>