drm/i915/gen9: fix typo when setting up the crtc scaler

This typo lead to the crtc scaler getting enabled incorrectly and an
evantual state checker mismatch about the scaler_id.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>