cmd/compile/internal/ssa: fix bad CL rebase

CL 142497 renamed "statictmp_N" to ".stmp_N", but missed an instance
that was added by CL 151498 (submitted between the window that CL
142497 was reviewed/tested and later rebased/merged).

Change-Id: I597ee59dfa40821c7af2881b47e06f84a8140ec8
Reviewed-on: https://go-review.googlesource.com/c/163877
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/compile/internal/ssa/writebarrier.go

@@ -384,7 +384,7 @@ func IsReadOnlyGlobalAddr(v *Value) bool {
 		return false
 	}
 	// See TODO in OpAddr case in IsSanitizerSafeAddr below.
-	return strings.HasPrefix(v.Aux.(*obj.LSym).Name, `"".statictmp_`)
+	return strings.HasPrefix(v.Aux.(*obj.LSym).Name, `""..stmp_`)
 }
 
 // IsNewObject reports whether v is a pointer to a freshly allocated & zeroed object at memory state mem.