PM / Domains: Free pm_subsys_data in error path in __pm_genpd_add_device()

The error path in __pm_genpd_add_device() didn't decrease the reference
to the struct pm_subsys_data.

Let's move the calls to dev_pm_get|put_subsys_data() into
genpd_alloc|free_dev_data() to fix this issue and thus prevent a
potential memory leakage.

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