hwmon: (ina238) Drop platform data support

hwmon: (ina238) Drop platform data support

There are no in-tree users of ina2xx platform data. Drop
support for it. The driver already supports device properties
which can be used as alternative if needed.

Also remove reference to the non-existing shunt_resistor sysfs
attribute from the driver documentation.

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>