x86: start64: Fix copyright message

There is a typo in this header. Fix it.
Signed-off-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NBin Meng <bmeng.cn@gmail.com>

arch/x86/cpu/start64.S

@@ -2,7 +2,7 @@
 /*
  * 64-bit x86 Startup Code
  *
- * (C) Copyright 216 Google, Inc
+ * Copyright 2019 Google, Inc
  * Written by Simon Glass <sjg@chromium.org>
  */