le_audio: Clear temporary cises assignement while disconnecting CISes

When all CISes from group are lost, temporary CIS list should be also
cleared. If list is not cleared before next CIS setup or CIS ID
assignement, code will hit issue with already assigned CISes.

Tag: #feature
Test: atest StateMachineTest#StreamReconfigureAfterCisLostTwoDevices
Bug: 263686512
Change-Id: Ib4a2b9ba41a060c3f5a5b0d8e3bf6d3dc8584063