Bluetooth: fix null ptr deref on hci_sync_conn_complete_evt

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: fix null ptr deref on hci_sync_conn_complete_evt This event is just specified for SCO and eSCO link types. On the reception of a HCI_Synchronous_Connection_Complete for a BDADDR of an existing LE connection, LE link type and a status that triggers the second case of the packet processing a NULL pointer dereference happens, as conn->link is NULL.