ACPI / scan: use kstrdup_const() in acpi_add_id()

Empirically, acpi_add_id is mostly called with string literals, so
using kstrdup_const for initializing struct acpi_hardware_id::id saves
a little run-time memory and a string copy.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/scan.c

@@ -1184,7 +1184,7 @@ static void acpi_add_id(struct acpi_device_pnp *pnp, const char *dev_id)
 	if (!id)
 		return;
 
-	id->id = kstrdup(dev_id, GFP_KERNEL);
+	id->id = kstrdup_const(dev_id, GFP_KERNEL);
 	if (!id->id) {
 		kfree(id);
 		return;
@@ -1322,7 +1322,7 @@ void acpi_free_pnp_ids(struct acpi_device_pnp *pnp)
 	struct acpi_hardware_id *id, *tmp;
 
 	list_for_each_entry_safe(id, tmp, &pnp->ids, list) {
-		kfree(id->id);
+		kfree_const(id->id);
 		kfree(id);
 	}
 	kfree(pnp->unique_id);