msm: qdsp5v2: memset stack buffer allocation.

This is needed to avoid garbage data in uninitialized variables.

Change-Id: Ie8c2b361ed1b8fbe47d5f0d372bcf5d8f776b5ed
CRs-Fixed: 554316
Signed-off-by: Asish Bhattacharya <asishb@codeaurora.org>