Use a FontSmoothingGamma value of 1.0

This is what the xcb plugin does, be consistent with it.

Change-Id: I5befa2de3ff514ca0c9196eb7137682586cec126
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>

src/client/qwaylandintegration.cpp

@@ -226,6 +226,13 @@ QVariant QWaylandIntegration::styleHint(StyleHint hint) const
     if (hint == ShowIsFullScreen && mDisplay->windowManagerIntegration())
         return mDisplay->windowManagerIntegration()->showIsFullScreen();
 
+    switch (hint) {
+    case QPlatformIntegration::FontSmoothingGamma:
+        return qreal(1.0);
+    default:
+        break;
+    }
+
     return QPlatformIntegration::styleHint(hint);
 }