msm: vidc: fix a race condition in OCMEM free function

OCMEM free function is called from both power collapse and
core release function. Due to race conditions this function
can be called simultaneously. This change adds mutex to prevent
race conditions.

Change-Id: Ic0efd3ff825b3f0eb8919228602c24eff28dddd3
Signed-off-by: Praneeth Paladugu <ppaladug@codeaurora.org>