msm: vidc: Ensure size of the data available before typecasting

Ensure the available data size with in the packet before type
casting from a smaller data type to larger data type in order
to avoid information leak or packet out of boundary access.

Change-Id: I8614a8b3f930c87af8aa49f77ea9d768a73ea203
Signed-off-by: Priyanka Gujjula <pgujjula@codeaurora.org>