CLEANUP: channel: fix comment in ci_putblk.

The comment is outdated and refer to an old code.

Should be backported until branch 1.5

(cherry picked from commit 147b3f05b5d5c3ec33f9d3ef2a6f79bbda1b3617)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/src/channel.c b/src/channel.c
index ba8ab63..c324673 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -152,8 +152,9 @@
 	max = channel_recv_limit(chn);
 	if (unlikely(len > max - c_data(chn))) {
 		/* we can't write this chunk right now because the buffer is
-		 * almost full or because the block is too large. Return the
-		 * available space or -2 if impossible.
+		 * almost full or because the block is too large. Returns
+		 * -3 if block is too large for this buffer. Or -1 if the
+		 * room left is not large enough.
 		 */
 		if (len > max)
 			return -3;