msm8916: set source on adev_open_input_stream

- Fixes FM recording where the app chooses the
  AUDIO_SOURCE_FM_RX source.  In this case, the
  HAL was being set to configure for the
  AUDIO_SOURCE_DEFAULT source, which selects
  the wrong input device in platform_get_input_snd_device.

Change-Id: Ic52679404664b5a2ce3e3433cd6296df78803f30