regulator: Export regulator_is_supported_voltage()

It's part of the driver interface so should be available to modules.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/regulator/core.c

@@ -1787,6 +1787,7 @@ int regulator_is_supported_voltage(struct regulator *regulator,
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(regulator_is_supported_voltage);
 
 static int _regulator_do_set_voltage(struct regulator_dev *rdev,
 				     int min_uV, int max_uV)