drm/i915: Don't populate plane->i9xx_plane for sprites

enum i9xx_plane_id namespace is not valid for any sprite plane,
so let's not even populate plane->i9xx_plane.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181005125817.22576-4-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/intel_sprite.c

@@ -1891,7 +1891,6 @@ intel_sprite_plane_create(struct drm_i915_private *dev_priv,
 	}
 
 	intel_plane->pipe = pipe;
-	intel_plane->i9xx_plane = plane;
 	intel_plane->id = PLANE_SPRITE0 + plane;
 	intel_plane->frontbuffer_bit = INTEL_FRONTBUFFER(pipe, intel_plane->id);