leaudio: Fix assert on group disconnect while CIG creation

This fixes race when group was disconnected while state machine was
waiting for CIG creation which leads to assert:

bluetooth: assertion 'leAudioDevice' failed - Shouldn't be called without an active device.

With this patch assert will not happen and CIG will be removed

Bug: 325627564
Test: atest bluetooth_le_audio_test
Flags: Exempt, regression verified with unit test, new test added
Change-Id: I21d29af4e487a609361fdf5fe6cfe1d6bf5de050