drm/msm/sde: avoid checking roi symmetry if zero mixers

Avoid checking whether the mixer ROI's are the same if the
number of mixers is zero.

Change-Id: Iefb92b2fc788a73187f0cfe0023dd7c07e603357
Signed-off-by: Clarence Ip <cip@codeaurora.org>
1 file changed