drm/i915: Pass old crtc state to skylake_scaler_disable()

To make life easier in the future let's pass the old crtc state
to skylake_scaler_disable() just like we already do for
for its ancestor ironlake_pfit_disable().

Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191213195217.15168-3-ville.syrjala@linux.intel.com
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>