hwmon: (ntc_thermistor) Drop get_ohm()

Nothing in the kernel (this driver) is using the callback to
read ohms directly. We always read a voltage and convert it
to a resistance. Drop this callback.

Cc: Peter Rosin <peda@axentia.se>
Cc: Chris Lesiak <chris.lesiak@licor.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20211125020841.3616359-3-linus.walleij@linaro.org


Signed-off-by: Guenter Roeck <linux@roeck-us.net>