PM / OPP: make _of_get_opp_desc_node() a static function

Since commit f47b72a1 ("PM / OPP: Move CONFIG_OF dependent code
in a separate file"), this function is defined and called only in
drivers/base/power/opp/of.c .
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/opp/of.c

@@ -198,7 +198,7 @@ void dev_pm_opp_of_remove_table(struct device *dev)
 EXPORT_SYMBOL_GPL(dev_pm_opp_of_remove_table);
 
 /* Returns opp descriptor node for a device, caller must do of_node_put() */
-struct device_node *_of_get_opp_desc_node(struct device *dev)
+static struct device_node *_of_get_opp_desc_node(struct device *dev)
 {
 	/*
 	 * TODO: Support for multiple OPP tables.

drivers/base/power/opp/opp.h

@@ -190,7 +190,6 @@ struct opp_table {
 /* Routines internal to opp core */
 struct opp_table *_find_opp_table(struct device *dev);
 struct opp_device *_add_opp_dev(const struct device *dev, struct opp_table *opp_table);
-struct device_node *_of_get_opp_desc_node(struct device *dev);
 void _dev_pm_opp_remove_table(struct device *dev, bool remove_all);
 struct dev_pm_opp *_allocate_opp(struct device *dev, struct opp_table **opp_table);
 int _opp_add(struct device *dev, struct dev_pm_opp *new_opp, struct opp_table *opp_table);