ASoc: msm: Synchronize access to compressed stream

Synchronize hw_ptr, appl_ptr access between the compressed
driver event handler and the ALSA core framework.

Change-Id: I118bfdf4a866cde05d9ebcd21f756da209b69cc5
CRs-Fixed: 501754
Signed-off-by: Haynes Mathew George <hgeorge@codeaurora.org>