leaudio: Fix handling invalid peer device

With this patch we make sure that le audio device is recognize as a part
of CSIS member if CSIS service is primary and is included by CAS on the
peer device.

Bug: 150670922
Tag: #feature
Sponsor: jpawlowski@
Test: atest --host bluetooth_le_audio_test bluetooth_le_audio_client_test

Change-Id: Ic454d8e586b4e42bc6af887479e5b824ac2afcc4