msm: camera: prevent invalid access through mmap

Disable access to invalid addresses through mmap.
Add appropriate range checks to ensure valid accesses
through framebuffer mmap. This prevents illegal
access into memory.

Change-Id: Ie053d9d8efe951b88f28b020dd9c2356e54723a7
CRs-Fixed: 475794
Signed-off-by: Manoj Rao <manojraj@codeaurora.org>