msm: vidc: Initialize kernel space stack variables

This change initializes kernel space stack variables
that are passed between kernel space and user space
using ioctls.
Non initialization of these variables may lead to
leakage of memory values from the kernel stack to
user space.

Change-Id: I5b45f3a7baf9c538fee2ec356cd8545f8b042b5e
CRs-fixed: 556771,563420
Signed-off-by: Deepak Verma <dverma@codeaurora.org>