msm_fb: display: silent blending error warning message

If there had no any pipe blending stage changes, then do not
call belnding set up to avoid unnecessary warning messges.

CRs-fixed: 467556
Change-Id: I07520b3b0917375c41405e736dcb9eb8a3daddc1
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>