disp: msm: dsi: add check for buffer length before copy

The change adds a check to make sure the length of bytes being
copied don't exceed the size of the destination buffer
causing an overflow.

Change-Id: Ib3ca3705e4179ccda1af11279e96e167baee6a3b
Signed-off-by: Satya Rama Aditya Pinapala <psraditya30@codeaurora.org>