Avoid magic numbers and use the introduced defines.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>