Eeschema: fix symbol library link not showing

In wxWidgets GTK, SetLabel() won't show anything. Seems like an old
wxWidgets issue:
https://forums.wxwidgets.org/viewtopic.php?t=20207

eeschema/dialogs/dialog_symbol_properties.cpp

@@ -497,7 +497,7 @@ bool DIALOG_SYMBOL_PROPERTIES::TransferDataToWindow()
     }
 
     // Set the symbol's library name.
-    m_tcLibraryID->SetLabelText( UnescapeString( m_symbol->GetLibId().Format() ) );
+    m_tcLibraryID->SetValue( UnescapeString( m_symbol->GetLibId().Format() ) );
 
     Layout();