ACPI / AC: constify DMI system id table

There is no need to have ac_dmi_table[] writeable, constify it.
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/ac.c

@@ -308,7 +308,7 @@ static int thinkpad_e530_quirk(const struct dmi_system_id *d)
 	return 0;
 }
 
-static struct dmi_system_id ac_dmi_table[] = {
+static const struct dmi_system_id ac_dmi_table[] = {
 	{
 	.callback = thinkpad_e530_quirk,
 	.ident = "thinkpad e530",