Mir: Fixed comment at conditional compilation macro.

src/video/mir/SDL_mirwindow.h

@@ -78,7 +78,7 @@ MIR_SetWindowMaximumSize(_THIS, SDL_Window* window);
 extern void
 MIR_SetWindowTitle(_THIS, SDL_Window* window);
 
-#endif /* _SDL_mirwindow */
+#endif /* _SDL_mirwindow_h */
 
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