msm: mdss: increase MDP ab vote to avoid under run

This change updates the bandwidth calculation for mdp3
hardware based on 8909 requirements, otherwise under run
is seen when USB is disconnected.

Change-Id: I49f7c225b57c43eca5ba8c6ac7b889e53cce6037
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>