drm/i915: Use crtc_clock in intel_dump_crtc_timings()

We want to dump the parameters given to the hardware, so let's use
crtc_clock here.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>