runtime: follow convention for generated code comment in fastlog2table

Follow the convertion (https://golang.org/s/generatedcode) for generated
code in fastlog2table.go

Change-Id: Ib40ae2848924d98afaf8d4fcaf180a4583edc3fe
Reviewed-on: https://go-review.googlesource.com/c/156817
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/fastlog2table.go

-// AUTO-GENERATED by mkfastlog2table.go
+// Code generated by mkfastlog2table.go; DO NOT EDIT.
 // Run go generate from src/runtime to update.
 // See mkfastlog2table.go for comments.
 

src/runtime/mkfastlog2table.go

@@ -20,7 +20,7 @@ import (
 func main() {
 	var buf bytes.Buffer
 
-	fmt.Fprintln(&buf, "// AUTO-GENERATED by mkfastlog2table.go")
+	fmt.Fprintln(&buf, "// Code generated by mkfastlog2table.go; DO NOT EDIT.")
 	fmt.Fprintln(&buf, "// Run go generate from src/runtime to update.")
 	fmt.Fprintln(&buf, "// See mkfastlog2table.go for comments.")
 	fmt.Fprintln(&buf)