msm: mdss: fix bandwidth vote release for dual-dsi cmd mode panels

For dual-dsi command mode panels, bandwidth(bw) vote is supposed to be
released once ping-pong done interrupt for both controller is received.
In current implementation, if secondary ctl finishes last, which is the
case most of the times, then bw release is called using secondary ctl.
But bw is calculated/stored using main ctl because of which bw vote is
never released as expected. Fix this by releasing bw vote using main ctl.

Change-Id: Iadbd150ed6a35478da2cb376e29b01e579a526b8
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>