test: fix bug headers

The letter is $A, not $O.
($O is set accidentally, but not for long.)

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5629045

test/fixedbugs/bug385_32.go

-// [ $O == 6 ] || errchk $G -e $D/$F.go
+// [ $A == 6 ] || errchk $G -e $D/$F.go
 
 // Copyright 2011 The Go Authors.  All rights reserved.
 // Use of this source code is governed by a BSD-style

test/fixedbugs/bug385_64.go

-// [ $O != 6 ]  || errchk $G -e $D/$F.go
+// [ $A != 6 ]  || errchk $G -e $D/$F.go
 
 // Copyright 2011 The Go Authors.  All rights reserved.
 // Use of this source code is governed by a BSD-style