ACPI / LPSS: set PM domain via helper setter

The commit 989561de9b51 ("PM / Domains: add setter for dev.pm_domain") changed
acpi_lpss.c module to use PM domain setter, though it missed one assignment.
Add it here.

Fixes: 989561de9b51 (PM / Domains: add setter for dev.pm_domain)
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/acpi/acpi_lpss.c b/drivers/acpi/acpi_lpss.c
index c570b1d..0872d5f 100644
--- a/drivers/acpi/acpi_lpss.c
+++ b/drivers/acpi/acpi_lpss.c
@@ -880,7 +880,7 @@
 		break;
 	case BUS_NOTIFY_DRIVER_NOT_BOUND:
 	case BUS_NOTIFY_UNBOUND_DRIVER:
-		pdev->dev.pm_domain = NULL;
+		dev_pm_domain_set(&pdev->dev, NULL);
 		break;
 	case BUS_NOTIFY_ADD_DEVICE:
 		dev_pm_domain_set(&pdev->dev, &acpi_lpss_pm_domain);