hal: Use usecase stream when audio source is Echo Ref

- Ensure that when the usecase stream's audio
  source is AUDIO_SOURCE_ECHO_REFERENCE, do not
  use the priority_in stream
- Ensures that the correct snd_device is used for
  echo ref usecases when recording concurrently
- Prevent mobile targets from having the priority
  input stream from being overwritten

Change-Id: I228fa116b6edb83fb6d7ec63504e635a41b8cdd0