Polish and fix qmlvideofx example

Change-Id: I30f6d7d2af784ba018a659a16aceb4876a4b1be6
Reviewed-by: hjk <qthjk@ovi.com>

examples/multimedia/video/qmlvideofx/qml/qmlvideofx/EffectBlackAndWhite.qml

@@ -52,5 +52,5 @@ Effect {
     // Transform slider values, and bind result to shader uniforms
     property real threshold: parameters.get(0).value
 
-    fragmentShaderFilename: "shaders/blackandwhite.fsh"
+    fragmentShaderFilename: "blackandwhite.fsh"
 }