btm_iso: Fix cig id in the OnCisEvent callback

When CIS is failed to be established, make sure that proper CIG id is
provided to the user of CIS module, as it might be used to match proper
CIS object.

Bug: 331775328
Test: atest net-test_btm_iso
Flag: Exempt, minor fix, regression tested with unit tests.
Change-Id: I379e43ecdafbf911ec1c094de24d4ff11e2576da