ACPI / PM: Assign the ->detach() callback when attaching the PM domain

As as preparation to simplify the detachment of devices from their PM
domains, we assign the ->detach() callback to genpd_dev_pm_detach().
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/device_pm.c

@@ -1072,6 +1072,8 @@ int acpi_dev_pm_attach(struct device *dev, bool power_on)
 		acpi_dev_pm_full_power(adev);
 		acpi_device_wakeup(adev, ACPI_STATE_S0, false);
 	}
+
+	dev->pm_domain->detach = acpi_dev_pm_detach;
 	return 0;
 }
 EXPORT_SYMBOL_GPL(acpi_dev_pm_attach);