msm: mdss: set vsync clock rate

Vsync clock rate is not set when vsync clock is enabled.
This cause command mode TE logic not works.

Change-Id: Ibf7dd07e53b2cd76ef30f13133368000c79ae149
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>