Simplify the code and avoid race condition caused by creating sysfs attributes
after creating the hwmon device.

Also replace SENSOR_DEVICE_ATTR with DEVICE_ATTR since the extra argument
is not used and SENSOR_DEVICE_ATTR is not needed.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>