msm: audio: qdsp6v2: Enhance EOS logic for Driver in Tunnel Mode

- Successful return of fsync funtion indicates EOS for the tunneled
  session, that is EOS cmd send and ack by QDSP6.
- A return val of error indicates fsync is interrupted by flush/
  stop/disable and EOS is not yet reached.

Change-Id: If57d075b0ddb09554c2df33c246590d528ded634
Signed-off-by: Sidipotu Ashok <sashok@codeaurora.org>