xcbutils: fix nativeFloor

The floor was not done in the X-native coordinate space but with double
scaling

BUG: 459373

src/utils/xcbutils.cpp

@@ -646,7 +646,7 @@ QSizeF fromXNative(const QSize &s)
 
 static qreal nativeFloor(qreal value)
 {
-    return std::floor(value / kwinApp()->xwaylandScale()) * kwinApp()->xwaylandScale();
+    return std::floor(value * kwinApp()->xwaylandScale()) / kwinApp()->xwaylandScale();
 }
 
 QRectF nativeFloor(const QRectF &rect)