Add missing precision qualifiers in qopenglwindow example

Make GLES implementations happy.

Change-Id: Ib389e379f23794eee0fa71ca26b863e56cee662e
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>

examples/opengl/qopenglwindow/background.frag

-uniform highp int currentTime;
+uniform int currentTime;
 uniform highp vec2 windowSize;
 
-float noise(vec2 co)
+highp float noise(highp vec2 co)
 {
     return 0.5 * fract(sin(dot(co.xy, vec2(12.9898,78.233))) * 43758.5453);
 }
 
-float curvSpeed()
+highp float curvSpeed()
 {
    return mod(float(currentTime), 1000000.0) / 500.0;
 }
 
-float curv()
+highp float curv()
 {
     return 1.0 - abs((gl_FragCoord.y / (windowSize.y / 10.0) - 5.0) - sin((gl_FragCoord.x / (windowSize.x/20.0)) - curvSpeed()));
 }
 
 void main()
 {
-    float coordNoise = noise(gl_FragCoord.xy);
-    float proximity = smoothstep(0.5, 1.0, (curv() + 1.0) * (coordNoise ));
+    highp float coordNoise = noise(gl_FragCoord.xy);
+    highp float proximity = smoothstep(0.5, 1.0, (curv() + 1.0) * (coordNoise ));
     gl_FragColor = vec4(coordNoise, coordNoise, coordNoise, 1.0) * proximity;
 }