msm_11ad: update bus voting according the arbitrated bandwidth

Bus voting set looking into Ib (instantaneous bandwidth) in the DTSI
instead of looking into Ab (arbitrated bandwidth).
Update the bus voting function to use the Ab.

Change-Id: I1107f883397d372085974cbd649a7208e31bfc0c
Signed-off-by: Alexei Avshalom Lazar <ailizaro@codeaurora.org>