cmd/compile: fix bug in vmatch1 list traversal nodeSeq change

Bug accidentally inserted in https://golang.org/cl/20210.  Doesn't seem
to make a difference, but restore original code anyhow.

Update #14473.

Change-Id: I9cf87987ff158e27c7231027819317cdde8c132c
Reviewed-on: https://go-review.googlesource.com/20401
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/compile/internal/gc/walk.go

@@ -2578,7 +2578,7 @@ func vmatch1(l *Node, r *Node) bool {
 	if vmatch1(l.Right, r) {
 		return true
 	}
-	for it := nodeSeqIterate(l); !it.Done(); it.Next() {
+	for it := nodeSeqIterate(l.List); !it.Done(); it.Next() {
 		if vmatch1(it.N(), r) {
 			return true
 		}