runtime/pprof/internal/profile: add copyright notice to profile_memmap.go

Change-Id: Ia511b0aadc87eb53e084d14cdb90ba4be958a43e
Reviewed-on: https://go-review.googlesource.com/32259Reviewed-by: Austin Clements <austin@google.com>

src/runtime/pprof/internal/profile/profile_memmap.go

+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
 package profile
 
 import (