msm: vidc: Avoid information leak while accessing the packet

Use trusted packet size on the received packet and check for
the size of the data received against the expected size
before accessing the packet.

Change-Id: I1bd6008249a0bf4edeec711ec8d23cf7b8dac1f1
Signed-off-by: Priyanka Gujjula <pgujjula@codeaurora.org>