drm/i915/cdclk: Reorder bxt_sanitize_cdclk()

Make the sequence of steps in bxt_sanitize_cdclk() more logical by
grouping things related to the check on the value of CDCLK_CTL into a
single "block". Also, this will make an upcoming change replacing that
block with a single function call easier to follow.

v2:
  - Improve body of commit message to be more self-contained.

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/20240105140538.183553-4-gustavo.sousa@intel.com