Prevent old callback events when track is recycled

When a track is reused from SoundPool and started again, the
previous callback events could be done after track started,
then the new playback will be stopped unintentionally.
Clear the old cblk flags when recycled track is started again
to avoid triggering unexpected callback events.

Bug: 112269355
Test: Playback with SoundPool frequently
Change-Id: I111b085d08b73c333fbb0fc2896efe1c013c584c