hwmon: (bt1-pvt) use generic polynomial functions

The polynomial calculation function was moved into lib/ to be able to
reuse it. Move over to this one.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20220401214032.3738095-3-michael@walle.cc


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