audio: restored front and back mic capture

Restored support for simultaneous capture of front and back mics
for voice recognition lost when switching to new audio HAL.

Also fixed problem in get_input_snd_device():
AUDIO_DEVICE_BIT_IN must be cleared in input_device before comparison
otherwise anding it with any input device value would return true.

Replaced adev->input_source and adev->in_device by adev->active_input:
this gives access to all info on the active input stream.

Change-Id: I03f02ffc120d6f69669618b4ab63cdcbd7b65877