msm: mdss: fix wrong mdp ib vote calculation

Fix missing assignment for the mdp ib bandwidth vote
calculation that was causing to skip the ib factor
and resulted in the wrong ib vote calculation.

Change-Id: I0289dc94040416e42543c192ad88ef246483c0d4
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>