hwmon: Convert remaining drivers to use SPDX identifier

This gets rid of the unnecessary license boilerplate, and avoids
having to deal with individual patches one by one.

No functional changes intended.

Reviewed-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>