msm: camera: Prevent buffer overread in write_logsync.

If userspace issues write with string of length 21 or more then
there is a chance that kernel will overread lbuf array.
This change makes sure that lbuf is NULL terminated.

Change-Id: I9ad6d5a607b2ff1f293512be9746ee554b076b10
Signed-off-by: Trishansh Bhardwaj <tbhardwa@codeaurora.org>