drm/msm/sde: initialize display info structure to zero

Display info structure is used by connector to report
display capabilities. Initialize structure to zero
to avoid reporting invalid values on unused display
capabilities.

Change-Id: I5b361d3349f2bc9f22f17ce684273ea8debd14e2
Signed-off-by: Alan Kwong <akwong@codeaurora.org>