Deregistering mixes before register mixes in connectMixes

When AudioFlinger binder dies and AudioService receives
onError/onAudioServerDied callback but AudioPolicy service is alive,
we get INVALID_OPERATION error because mixes was already registered.
This causes calling release on AudioPolicyProxy.

Test: Manual
Bug: 380092408

Change-Id: I4e5c6e3d3aace03f02f312fda26e5696ac090d04