hwmon: (k8temp) update to use new hwmon registration API

hwmon: (k8temp) update to use new hwmon registration API

Removes:
- hwmon_dev from k8temp_data struct, as that is now passed
  to callbacks, anyway.
- other k8temp_data struct fields, too.
- k8temp_update_device()

Also reduces binary size:
   text    data     bss     dec     hex filename
   4139    1448       0    5587    15d3 drivers/hwmon/k8temp.ko.bak
   3103    1220       0    4323    10e3 drivers/hwmon/k8temp.ko

Signed-off-by: Robert Karszniewicz <avoidr@firemail.cc>
Signed-off-by: Robert Karszniewicz <avoidr@riseup.net>
Link: https://lore.kernel.org/r/20190721120051.28064-1-avoidr@riseup.net
Signed-off-by: Guenter Roeck <linux@roeck-us.net>