hwmon: (coretemp) Convert to use devm_hwmon_device_register_with_groups

Simplify code, reduce code size, and attach sysfs attributes to hwmon device.

For this driver, the only attribute created is the name attribute.
Other attributes are still created and removed dynamically as cores
are added or removed.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Tested-by: Jean Delvare <jdelvare@suse.de>