drm/msm/sde: check for null commit during secure transitions

In video mode, NULL commit is required for secure to non-secure
or non secure to secure transitions. Atomic check failure is
returned if this condition fails.

Change-Id: I977410e5a3846de87be3d23e04fa59929c8c5839
Signed-off-by: Raviteja Tamatam <travitej@codeaurora.org>