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.

CRs-fixed: 556771,563420

Change-Id: I2b6f92a7fcf712b29505ba8e38499084c4fbf194
Signed-off-by: Deepak Verma <dverma@codeaurora.org>