ASoC: compr: timestamp fix for non-gapless mode

Cache last known playback timestamp before resetting the
in use session in preparation for possible re-use of the
same session.

Change-Id: Id422f5654960818c159f9f07d5af3c497192bae2
Signed-off-by: Haynes Mathew George <hgeorge@codeaurora.org>
Signed-off-by: Dhananjay Kumar <dhakumar@codeaurora.org>