regulator: change devm_regulator_get_enable_optional() stub to return Ok

The devm_regulator_get_enable_optional() should be a 'call and forget'
API, meaning, when it is used to enable the regulators, the API does not
provide a handle to do any further control of the regulators. It gives
no real benefit to return an error from the stub if CONFIG_REGULATOR is
not set.

On the contrary, returning an error is causing problems to drivers when
hardware is such it works out just fine with no regulator control.
Returning an error forces drivers to specifically handle the case where
CONFIG_REGULATOR is not set, making the mere existence of the stub
questionalble.

Change the stub implementation for the
devm_regulator_get_enable_optional() to return Ok so drivers do not
separately handle the case where the CONFIG_REGULATOR is not set.
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Fixes: da279e69 ("regulator: Add devm helpers for get and enable")
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/ZiedtOE00Zozd3XO@fedoraSigned-off-by: Mark Brown <broonie@kernel.org>

include/linux/regulator/consumer.h

@@ -326,7 +326,7 @@ static inline int devm_regulator_get_enable(struct device *dev, const char *id)
 static inline int devm_regulator_get_enable_optional(struct device *dev,
 						     const char *id)
 {
-	return -ENODEV;
+	return 0;
 }
 
 static inline struct regulator *__must_check