AudioTrack: Refine the wait for volume ramp on pause

This avoids pop due to a flush immediately after pause
done by MediaPlayer.

Test: Play YT Music, adjust notification volume in settings and
      see if there is a pop at the end of playback.
Bug: 202376326
Merged-In: I8bfede65bd4e8daa721d25af1ade44382937df95
Change-Id: I8bfede65bd4e8daa721d25af1ade44382937df95
(cherry picked from commit d87a53a3)