drm/i915: Flatten intel_ddi_{enable,disable}_transcoder_clock()

Use an early return to get rid of the extra indentation level
in intel_ddi_{enable,disable}_transcoder_clock().

Also unify the platform handling in between the two while at
it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230213225258.2127-3-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>