leaudio: Fix for handling multiple LeAudio headsets

Make sure to get proper CIG ID when handling CisEstablished event

Bug: 241883130
Test: atest BluetoothInstrumentationTests
Test: manual: connect two LeAudio headsets and make a phone call
Tag: #feature
Merged-In: Ic945638c6c3a9e0e87a868bc26d5f6a3590a51ff
Change-Id: Ic945638c6c3a9e0e87a868bc26d5f6a3590a51ff
(cherry picked from commit 45952e25)