regulator: core: Ensure we lock all regulators

The latest workaround for the lockdep interface's not using the second
argument of mutex_lock_nested() changed the loop missed locking the last
regulator due to a thinko with the loop termination condition exiting
one regulator too soon.
Reported-by: Tyler Baker <tyler.baker@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/core.c

@@ -141,7 +141,7 @@ static void regulator_lock_supply(struct regulator_dev *rdev)
 	int i;
 
 	mutex_lock(&rdev->mutex);
-	for (i = 1; rdev->supply; rdev = rdev->supply->rdev, i++)
+	for (i = 1; rdev; rdev = rdev->supply->rdev, i++)
 		mutex_lock_nested(&rdev->mutex, i);
 }