drm/msm: do not report error when data block is not present

There might be no data blocks in certain CTA extensions, so
avoid reporting error in these cases.

CRs-Fixed: 2291150
Change-Id: I8546c8c45d01d878e198604d6e9cebbc32fa7a0d
Signed-off-by: Ray Zhang <rayz@codeaurora.org>