fix old GCC build

after my commit 10749bbf
"remove the last of the OUString #defines in header files"

Change-Id: I7666cfb28d8a28d541c9d7a51f014ebe53c50551

chart2/source/model/filter/XMLFilter.cxx

@@ -809,7 +809,7 @@ void XMLReportFilterHelper::isOasisFormat(const Sequence< beans::PropertyValue >
 }
 OUString XMLReportFilterHelper::getMediaType(bool )
 {
-    return MIMETYPE_OASIS_OPENDOCUMENT_REPORT_CHART_ASCII;
+    return OUString(MIMETYPE_OASIS_OPENDOCUMENT_REPORT_CHART_ASCII);
 }
 
 } //  namespace chart

chart2/source/model/main/ChartModel.cxx

@@ -324,7 +324,7 @@ OUString SAL_CALL ChartModel::getImplementationName()
 
 OUString ChartModel::getImplementationName_Static()
 {
-    return CHART_MODEL_SERVICE_IMPLEMENTATION_NAME;
+    return OUString(CHART_MODEL_SERVICE_IMPLEMENTATION_NAME);
 }
 
 sal_Bool SAL_CALL ChartModel::supportsService( const OUString& rServiceName )

chart2/source/view/main/ChartView.cxx

@@ -1396,7 +1396,7 @@ OUString SAL_CALL ChartView::getImplementationName()
 
 OUString ChartView::getImplementationName_Static()
 {
-    return CHART_VIEW_SERVICE_IMPLEMENTATION_NAME;
+    return OUString(CHART_VIEW_SERVICE_IMPLEMENTATION_NAME);
 }
 
 sal_Bool SAL_CALL ChartView::supportsService( const OUString& rServiceName )