sync: update comments for Once.done

Sync with CL 666895.

Change-Id: I49c4a7f88d87cee9c30a858facd3cd8348efdf94
GitHub-Last-Rev: 88ac1c9
GitHub-Pull-Request: #76026
Reviewed-on: https://go-review.googlesource.com/c/go/+/714360
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Jorropo <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Reviewed-by: David Chase <[email protected]>
Reviewed-by: Jorropo <[email protected]>

Author: callthingsoff

src/sync/once.go

@@ -52,7 +52,7 @@ type Once struct {
 func (o *Once) Do(f func()) {
 	// Note: Here is an incorrect implementation of Do:
 	//
-	//	if o.done.CompareAndSwap(0, 1) {
+	//	if o.done.CompareAndSwap(false, true) {
 	//		f()
 	//	}
 	//