drm/msm/sde: remove error message from optional settings

vbif ot limit setting is optional. Convert error message to
debug message because target does not specify the ot
limit during bring up time.

Change-Id: I0f096a3345c18598576ad55601d53027ce2a6f4f
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>