make sure variable is declared in correct scope

https://lgtm.com/projects/g/mrdoob/three.js/snapshot/32fd13b241a1001af0045c3263d17dc2e133f482/files/examples/webgl_postprocessing_pixel.html?sort=name&dir=ASC&mode=heatmap&excluded=false#xe096d56c13b4e91d:1

examples/webgl_postprocessing_pixel.html

@@ -54,7 +54,7 @@
 
 		<script>
 
-			var camera, scene, renderer, gui, composer;
+			var camera, scene, renderer, gui, composer,controls;
 			var pixelPass, params;
 
 			var group;