regulator: Let drivers know when they use the stub API

Have the stub variant of regulator_get() return NULL, so that drivers
can (but still don't have to) handle this case specifically.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Jerome Oufella <jerome.oufella@savoirfairelinux.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>

include/linux/regulator/consumer.h

@@ -183,9 +183,13 @@ static inline struct regulator *__must_check regulator_get(struct device *dev,
 {
 	/* Nothing except the stubbed out regulator API should be
 	 * looking at the value except to check if it is an error
-	 * value so the actual return value doesn't matter.
+	 * value. Drivers are free to handle NULL specifically by
+	 * skipping all regulator API calls, but they don't have to.
+	 * Drivers which don't, should make sure they properly handle
+	 * corner cases of the API, such as regulator_get_voltage()
+	 * returning 0.
 	 */
-	return (struct regulator *)id;
+	return NULL;
 }
 static inline void regulator_put(struct regulator *regulator)
 {