regulator: add missing defintion regulator_is_supported_voltage

This definition is missing when CONFIG_REGULATOR is not defined.
This causes compiler errors when compiling sdhci.c.  This can
be worked around by adding #ifdef CONFIG_REGULATOR .. #endif
but since other definitions are there we have defined the missing
definition
Signed-off-by: Philip Rakity <prakity@marvell.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

include/linux/regulator/consumer.h

@@ -294,6 +294,12 @@ static inline int regulator_get_voltage(struct regulator *regulator)
 	return -EINVAL;
 }
 
+static inline int regulator_is_supported_voltage(struct regulator *regulator,
+				   int min_uV, int max_uV)
+{
+	return 0;
+}
+
 static inline int regulator_set_current_limit(struct regulator *regulator,
 					     int min_uA, int max_uA)
 {