msm: mdss: update the clocks for slave controller

While updating refresh rate through dynamic fps node,
clock calculations are still needed for the slave controller
and enablement of clock for slave controller is not needed.
This change fixes clock updation of slave controller with
dynamic fps feature enabled.

Change-Id: Ibabe9bddba0633cc9a3441207f39a2f3fa7a8f71
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>