PM / Domains: pdd->dev can't be NULL in genpd_dev_pm_qos_notifier()

The pm_domain_data (pdd) pointer is set from genpd_alloc_dev_data() and
pdd->dev is guaranteed to be valid. There is no need to check pdd and
pdd->dev in rest of the code as pdd->dev will always be valid for a non
NULL pdd pointer.

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