Bluetooth: hci_sync: Fix attempting to send HCI_Disconnect to BIS handle

BIS/PA connections do have their own cleanup proceedure which are
performed by hci_conn_cleanup/bis_cleanup.

Fixes: 23205562 ("Bluetooth: separate CIS_LINK and BIS_LINK link types")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>