alsa-endpoint: add a FIXME for some missing code

We call setup_alsa_ucm_endpoint() before the
setup_alsa_fallback_endpoint(), but this function always returns
-ENOTSUP. Add a FIXME comment to make this more obvious.

src/examples/media-session/alsa-endpoint.c

@@ -610,6 +610,8 @@ static int setup_alsa_ucm_endpoint(struct device *device)
 		pw_log_debug("verb: %s", verb_list[i]);
 	}
 
+	/* FIXME: implement this */
+
 	snd_use_case_free_list(verb_list, num_verbs);
 
 	res = -ENOTSUP;