drm/msm/sde: ignore scaler v2 data if not enabled

The incoming scaler v2 user data isn't guaranteed to be
valid if the 'enable' field is set to zero, so ignore
the entire structure unless the enable is explicitly set
to a non-zero value.

CRs-Fixed: 2052501
Change-Id: Ieeb24122a5caffcd7361007e52219cee94e33eee
Signed-off-by: Clarence Ip <cip@codeaurora.org>