NCT6793D is register compatible with NCT6792D.

Also move nct6775_sio_names[] closer to enum kinds to simplify
adding new chips.
Tested-by: Grazvydas Ignotas <notasas@gmail.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>