Fix mistaken use of `m_width`

This is a protected var in Linux but doesn't exist in Mac/MSW.  We use
the new m_fieldsSize

eeschema/dialogs/dialog_symbol_properties.cpp

@@ -797,8 +797,7 @@ void DIALOG_SYMBOL_PROPERTIES::OnGridEditorShown( wxGridEvent& aEvent )
 
     /// Queue up an event to ensure the widget gets resized if the editor needs it
     wxSizeEvent *evt = new wxSizeEvent();
-    evt->SetSize( wxSize( m_width + 1, -1 ) );
-
+    evt->SetSize( m_fieldsSize +  wxSize( 1, 1 ) );
     wxQueueEvent( m_fieldsGrid, evt );
 
     wxSizeEvent *frmEvt = new wxSizeEvent();