ACPI / video: skip evaluating _DOD when it does not exist

Some system supports hybrid graphics and its discrete VGA
does not have any connectors and therefore has no _DOD method.

BugLink: http://bugs.launchpad.net/bugs/1634607Signed-off-by: Alex Hung <alex.hung@canonical.com>
Reviewed-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
(cherry picked from commit e34fbbac)
Signed-off-by: Alex Hung <alex.hung@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

drivers/acpi/acpi_video.c

@@ -1211,6 +1211,9 @@ static int acpi_video_device_enumerate(struct acpi_video_bus *video)
 	union acpi_object *dod = NULL;
 	union acpi_object *obj;
 
+	if (!video->cap._DOD)
+		return AE_NOT_EXIST;
+
 	status = acpi_evaluate_object(video->device->handle, "_DOD", NULL, &buffer);
 	if (!ACPI_SUCCESS(status)) {
 		ACPI_EXCEPTION((AE_INFO, status, "Evaluating _DOD"));