CLEANUP: quic: complete comment on qcs_try_to_consume

Specify the return value usage.
diff --git a/src/xprt_quic.c b/src/xprt_quic.c
index 0af176e..56c6885 100644
--- a/src/xprt_quic.c
+++ b/src/xprt_quic.c
@@ -1400,7 +1400,8 @@
 }
 
 /* Remove from <qcs> stream the acknowledged frames.
- * Never fails.
+ *
+ * Returns 1 if at least one frame was removed else 0.
  */
 static int qcs_try_to_consume(struct qcs *qcs)
 {