x86: cpu: Make the vendor table const

This does not need to be modified at run-time, so make it const.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/x86/cpu/cpu.c

@@ -71,7 +71,7 @@ struct cpuinfo_x86 {
  * List of cpu vendor strings along with their normalized
  * id values.
  */
-static struct {
+static const struct {
 	int vendor;
 	const char *name;
 } x86_vendors[] = {