hwmon: (ads1015) Fix file leak in probe function

An error while creating sysfs attribute files in the driver's probe function
results in an error abort, but already created files are not removed. This patch
fixes the problem.

Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Cc: stable@vger.kernel.org # 3.0+
Cc: Dirk Eibach <eibach@gdsys.de>
Acked-by: Jean Delvare <khali@linux-fr.org>