Use kHz units in vlv cdclk code since that's more customary.

Also replace the precomputed 90% values with *9/10 computation
for extra clarity.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>