disp: msm: sde: update clk rate for perf mode

This updates the mdp clock rate immediately,
instead of waiting for the next frame trigger.

Change-Id: I5d58a1f1200fff143b363e89e8c49f6e7d8d14c7
Signed-off-by: Nilaan Gunabalachandran <ngunabal@codeaurora.org>