msm: mdss: update mipi frame rate after new fps is set

With dynamic refresh feature enabled in immediate clock
update mode, update the mipi frame rate as well to the
new rate.

This is required for calculating sleep time for retire
fence count to be accurate.

Change-Id: I9fa9b420df8f1496d0bb4dab3d3ee50d35630394
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>