Audio: Fix for pop noise when switching FM playback from mute to unmute

 - While unmuting FM stream AudioService applies default device volume
   followed by device specific volume, which is appearing as pop noise
   when device specific volume  is less than default device volume.
 - Fix is to apply only device specific volume when FM is active

Change-Id: I10855f0a2ccf53f0d98dfea80caffa232462adb8