audio_policy : Fix for incorrect input device selection

BLUETOOTH_SCO_HEADSET is not avaibale in input devices list
for recording usecases. Add the same to allow VOIP applications
to select BLUETOOTH_SCO_HEADSET as input device when
BT is connected.

Change-Id: I5d5010ab396f85bf58573943c91fd815f39f57c1
CRs-fixed: 712950