drm/msm: dsi: Return errors whan dt parsing fails

If dt parsing fails, we should return an error instead of pretending
everything completed successfully.

Cc: Doug Anderson <dianders@chromium.org>
Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>

Signed-off-by: Rob Clark <robdclark@gmail.com>