Bluetooth: hci_sync: Fix missing static warnings

This fixes the following warnings:

>> net/bluetooth/hci_sync.c:1333:5: warning: no previous prototype for
'hci_scan_disable_sync' [-Wmissing-prototypes]
    1333 | int hci_scan_disable_sync(struct hci_dev *hdev, bool rpa_le_conn)
         |     ^~~~~~~~~~~~~~~~~~~~~
>> net/bluetooth/hci_sync.c:1762:5: warning: no previous prototype for
'hci_passive_scan_sync' [-Wmissing-prototypes]
    1762 | int hci_passive_scan_sync(struct hci_dev *hdev)
         |     ^~~~~~~~~~~~~~~~~~~~~

Fixes: e8907f76 ("Bluetooth: hci_sync: Make use of hci_cmd_sync_queue set 3")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>