SQL TDS fix missing override keyword

Plugin failed to build with clang due to missing Q_DECL_OVERRIDE

Change-Id: Idad54f3f0ea7403c388b39189d86cfab10f9fb04
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

src/plugins/sqldrivers/tds/qsql_tds.cpp

@@ -163,7 +163,7 @@ class QTDSResult : public QSqlCachedResult
 public:
     explicit QTDSResult(const QTDSDriver* db);
     ~QTDSResult();
-    QVariant handle() const;
+    QVariant handle() const Q_DECL_OVERRIDE;
 
 protected:
     void cleanup();