msm: camera: Add validation check for cpu buffers before accessing

Add validation check before accessing the packets and configs from
the buffers.

Change-Id: I7b55fb01f0c679415e09680454d58cc545d9d5ff
Signed-off-by: Abhilash Kumar <krabhi@codeaurora.org>
Signed-off-by: Raja Mallik <rmallik@codeaurora.org>