hwmon: (ina238) Only configure calibration and shunt registers if needed

hwmon: (ina238) Only configure calibration and shunt registers if needed

Prepare for supporting chips with internal shunt resistor by only setting
calibration and shunt resistor registers if no current LSB is configured.

Do not display a log message during probe if a chip does not have shunt
and gain registers since those would otherwise display 0, and a message
just indicating that the driver was loaded would be just noise.

Reviewed-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Tested-by: Chris Packham <chris.packham@alliedtelesis.co.nz> # INA780
Signed-off-by: Guenter Roeck <linux@roeck-us.net>