Bluetooth: hci_event: Disconnect device when BIG sync is lost

When a BIG sync is lost, the device should be set to "disconnected".
This ensures symmetry with the ISO path setup, where the device is
marked as "connected" once the path is established. Without this
change, the device state remains inconsistent and may lead to a
memory leak.

Fixes: b2a5f2e1 ("Bluetooth: hci_event: Add support for handling LE BIG Sync Lost event")
Signed-off-by: Yang Li <yang.li@amlogic.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>