accessibility: Small optimisation in AccessibleTabListBox

Change-Id: Idf351923a57cf608dd4945e3ce639ba8011ecdbb
Reviewed-on: https://gerrit.libreoffice.org/49922Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

accessibility/source/extended/accessibletablistbox.cxx

@@ -99,10 +99,10 @@ namespace accessibility
         if (nChildIndex == 0)
         {
             //! so far the actual implementation object only supports column headers
-            xRet = implGetFixedChild( ::svt::BBINDEX_COLUMNHEADERBAR );
+            xRet = implGetHeaderBar( ::svt::BBTYPE_COLUMNHEADERBAR );
         }
         else if (nChildIndex == 1)
-            xRet = implGetFixedChild( ::svt::BBINDEX_TABLE );
+            xRet = implGetTable();
 
         if ( !xRet.is() )
             throw RuntimeException();