add clearCoatNormal context only to physical

src/renderers/shaders/ShaderChunk/common.glsl.js

@@ -39,7 +39,9 @@ struct GeometricContext {
 	vec3 position;
 	vec3 normal;
 	vec3 viewDir;
+#ifdef PHYSICAL
 	vec3 clearCoatNormal;
+#endif
 };
 
 vec3 transformDirection( in vec3 dir, in mat4 matrix ) {