drm/i915/cdclk: Re-use bxt_cdclk_ctl() when sanitizing

The function bxt_cdclk_ctl() is responsible for deriving the value for
CDCLK_CTL; use it instead of repeating the same logic.

v2:
  - Use a better commit message body by making it more self-contained
    and not referring to stuff from the subject line. (Matt)

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240105140538.183553-5-gustavo.sousa@intel.com