vlc_dialog: fix doxygen warnings

include/vlc_dialog.h:383: warning: The following parameter of vlc_dialog_provider_set_callbacks(vlc_object_t *p_obj, const vlc_dialog_cbs *p_cbs, void *p_data) is not documented:
      parameter 'p_obj'

    include/vlc_dialog.h:395: warning: The following parameter of vlc_dialog_provider_set_error_callback(vlc_object_t *p_obj, vlc_dialog_error_cbs p_cbs, void *p_data) is not documented:
      parameter 'p_obj'

    include/vlc_dialog.h:482: warning: The following parameter of vlc_dialog_provider_set_ext_callback(vlc_object_t *p_obj, vlc_dialog_ext_update_cb pf_update, void *p_data) is not documented:
      parameter 'p_obj'

include/vlc_dialog.h

@@ -381,6 +381,7 @@ typedef void (*vlc_dialog_error_cbs)(void *p_data, const char *psz_title, const
 /**
  * Register callbacks to handle VLC dialogs
  *
+ * @param p_obj the VLC object to get the dialog provider from
  * @param p_cbs a pointer to callbacks, or NULL to unregister callbacks.
  * @param p_data opaque pointer for the callback
  */
@@ -395,6 +396,7 @@ vlc_dialog_provider_set_callbacks(vlc_object_t *p_obj,
  *
  * @version LibVLC 4.0.0 and later.
  *
+ * @param p_obj the VLC object to get the dialog provider from
  * @param p_cbs a pointer to the callback, or NULL to unregister the callback.
  * @param p_data opaque pointer for the callback
  */
@@ -480,6 +482,7 @@ typedef void (*vlc_dialog_ext_update_cb)(extension_dialog_t *p_ext_dialog,
 /**
  * Register a callback for VLC extension dialog
  *
+ * @param p_obj a VLC object to get the libvlc instance from
  * @param pf_update a pointer to the update callback, or NULL to unregister
  * callback
  * @param p_data opaque pointer for the callback