asus_acpi: fix possible double free (found by Coverity)

Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/drivers/acpi/asus_acpi.c b/drivers/acpi/asus_acpi.c
index 9c4bd22..86fd142 100644
--- a/drivers/acpi/asus_acpi.c
+++ b/drivers/acpi/asus_acpi.c
@@ -1192,6 +1192,7 @@
 			break;
 		default:
 			kfree(model);
+			model = NULL;
 			break;
 		}
 	}