hal: Fix digital USB headset combo device

 * Digital USB output was not handled in this case. Add it.

Change-Id: I8e984a2cf545dabdc6dc538b75e8ca7221fb6688
hal: Fix arguments passed to set_echo_reference

* set_echo_reference function takes (struct audio_device *, bool) but is
  being passed (struct mixer *, int) instead.

Change-Id: I3b4fab2b2d266eebac0d5bab80f7a377d442d8fa