QmlDesigner: Fix resize controller assign operator

Change-Id: Id9d00c0fa0c1f5d3780191dbe912c5c7c581e549
Reviewed-by: hjk <hjk121@nokiamail.com>
Reviewed-by: Christian Stenger <christian.stenger@digia.com>

src/plugins/qmldesigner/components/formeditor/resizecontroller.cpp

@@ -165,6 +165,8 @@ ResizeController::~ResizeController()
 ResizeController &ResizeController::operator =(const ResizeController &other)
 {
     m_data = other.m_data;
+
+    return *this;
 }