Do not query max samples on gles

Querying GL_MAX_SAMPLES is not supported in GLES2.

Avoiding the call also makes us play nice with Mesa in debug
mode since it gets rid of the warnings about the failing
glGetIntegerv call.

Change-Id: I05e501cc11af41a54fefc34ab919c5191e4f3f0a
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>

src/gui/opengl/qopenglframebufferobject.cpp

@@ -432,9 +432,11 @@ void QOpenGLFramebufferObjectPrivate::init(QOpenGLFramebufferObject *, const QSi
         samples = 0;
     }
 
+#ifndef QT_OPENGL_ES_2
     GLint maxSamples;
     glGetIntegerv(GL_MAX_SAMPLES, &maxSamples);
     samples = qBound(0, int(samples), int(maxSamples));
+#endif
 
     size = sz;
     target = texture_target;