le_audio_software: Fix updating Audio HAL configuration

When set member disconnects AudioHAL is notified about configuration
update.
This patch fixes scenerio, when this configuration update could contain
invalid LC3 configuration.

Bug: 396312681
Flag: Exempt, day-to-day fix. Regression covered with unit test
Test: mmm packages/modules/Bluetooth
Test: manual testing verified with QA
Change-Id: Ie94f911cb343fe2551728199c08c61bc0dfd6cd6