Fix clang error: 'pointer_options' defined as a struct here but previously declared as a class; this is valid, but may result in linker errors under the Microsoft C++ ABI [-Werror,-Wmismatched-tags]

src/frontend/mame/ui/ui.cpp

@@ -188,7 +188,7 @@ struct mame_ui_manager::active_pointer
 };
 
 
-struct mame_ui_manager::pointer_options
+class mame_ui_manager::pointer_options
 {
 public:
 	pointer_options()