msm: qdsp6v2: memset stack buffer allocation.

This is needed to avoid garbage data in uninitialized variables.

Change-Id: Ifbe149c25c0c824b74d45e30d85a1c50670a81e0
CRs-Fixed: 554301
Signed-off-by: Asish Bhattacharya <asishb@codeaurora.org>