policy: fix voice volume is mismatch after headset remove

During voice call, when headset remove, new device of primary
output is first set to handset, and voice volume is also
calculated in handset. Later other outputs loop to select new
device and caculate volume in new device. Due to inactive output
selectes AUDIO_DEVICE_NONE, it uses previous device and set wrong
voice volume.

Fix it by add check to avoid applying volume for inactive output.

Change-Id: Icc0dd9e1f00cafd6548d20c678c882e770effc0d