Examples: Fix `webgpu_water` GUI (#31014)

examples/webgpu_water.html

@@ -149,7 +149,7 @@
 				// gui
 
 				const gui = new GUI();
-				const waterNode = water.material.fragmentNode;
+				const waterNode = water.material.colorNode;
 
 				gui.addColor( params, 'color' ).onChange( function ( value ) {