opp: core: Add missing export for dev_pm_opp_adjust_voltage

Export dev_pm_opp_adjust_voltage() as it may be used by modules later
on.

Signed-off-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
[ Viresh: Rewrote commit log ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

drivers/opp/core.c

@@ -2271,6 +2271,7 @@ adjust_put_table:
 	dev_pm_opp_put_opp_table(opp_table);
 	return r;
 }
+EXPORT_SYMBOL_GPL(dev_pm_opp_adjust_voltage);
 
 /**
  * dev_pm_opp_enable() - Enable a specific OPP