realtek: thermal: separate initialization/operation

realtek: thermal: separate initialization/operation

The driver uses lazy initialization - during first temperature
get. Checking enabled status over and over again does not make
sense. Provide separate setup functions for this. With this split
the error handling will be improved. If initialization fails, the
sensor will not be registered at all.

While we are here fix some minor typos.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/23405
Signed-off-by: Robert Marko <robimarko@gmail.com>