Cycles microdisplacement: preserve smooth normals for linear subdivison

This way we prevent cracks in the model due to discontinuous normals, by using
smooth normals for displacement instead of always getting flat normals after
linear subdivision.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D1916

intern/cycles/subd/subd_split.cpp

@@ -50,7 +50,7 @@ float3 DiagSplit::to_world(Patch *patch, float2 uv)
 {
 	float3 P;
 
-	patch->eval(&P, NULL, NULL, uv.x, uv.y);
+	patch->eval(&P, NULL, NULL, NULL, uv.x, uv.y);
 	if(params.camera)
 		P = transform_point(&params.objecttoworld, P);