Add 'return' comment to SDL_ClearClipboardData

include/SDL3/SDL_clipboard.h

@@ -197,6 +197,9 @@ extern DECLSPEC int SDLCALL SDL_SetClipboardData(SDL_ClipboardDataCallback callb
 /**
  * Clear the clipboard data
  *
+ * \returns 0 on success or a negative error code on failure; call
+ *          SDL_GetError() for more information.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_SetClipboardData