PM / Domains: Check for existing PM domain in dev_pm_domain_attach()

Instead of checking if an existing PM domain pointer has been assigned in
genpd_dev_pm_attach() and acpi_dev_pm_attach(), move the check to the
common path in dev_pm_domain_attach(), thus potentially avoid one
unnecessary check.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/common.c

@@ -104,6 +104,9 @@ int dev_pm_domain_attach(struct device *dev, bool power_on)
 {
 	int ret;
 
+	if (dev->pm_domain)
+		return -EEXIST;
+
 	ret = acpi_dev_pm_attach(dev, power_on);
 	if (ret)
 		ret = genpd_dev_pm_attach(dev);