PM / OPP: Make local function ti_opp_supply_set_opp() static

Fixes the following sparse warning:

drivers/opp/ti-opp-supply.c:276:5: warning:
 symbol 'ti_opp_supply_set_opp' was not declared. Should it be static?
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/opp/ti-opp-supply.c

@@ -273,7 +273,7 @@ static int _opp_set_voltage(struct device *dev,
  *
  * Return: If successful, 0, else appropriate error value.
  */
-int ti_opp_supply_set_opp(struct dev_pm_set_opp_data *data)
+static int ti_opp_supply_set_opp(struct dev_pm_set_opp_data *data)
 {
 	struct dev_pm_opp_supply *old_supply_vdd = &data->old_opp.supplies[0];
 	struct dev_pm_opp_supply *old_supply_vbb = &data->old_opp.supplies[1];