drm/i915: Make i830 .get_cdclk() assignment less confusing

drm/i915: Make i830 .get_cdclk() assignment less confusing

Explicitly check for i830 when assigning the .get_cdclk() vfunc,
and then deal with the case of not having assigned the vfunc
separately. Less confusing, and gets rid of the checkpatch complaint
about using {} on one branch but not the others.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200714152626.380-3-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>