PM / Domains: Remove redundant pm_runtime_get|put*() in pm_genpd_prepare()

The PM core increases and decreases the runtime PM usage count in the
system PM prepare phase. This makes some of the pm_runtime_get|put*()
calls in pm_genpd_prepare() redundant, so let's remove them.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>