disp: msm: add check for buffer length before copy

Length of the buffer to be copied is checked
against both source and destination buffer lengths
before copying. This ensures that there is  no
buffer overflow while reading as well as writing.

Change-Id: Ie261a0d3f4917a94a7348ac5aa7e188130aed865
Signed-off-by: Ravikanth Tuniki <rtunik@codeaurora.org>
Signed-off-by: Rahul Sharma <rahsha@codeaurora.org>