drm/msm/sde: print error only if catalog property is mandatory

Current validation function outputs error if non-mandatory property
does not exist in device tree. Change validation function to print
error only if property is mandatory.

Change-Id: I5b93c3896e2831e6037378e8f090202ed923796a
Signed-off-by: Alan Kwong <akwong@codeaurora.org>
1 file changed