hwmon: (ina238) Drop pointless power attribute check on attribute writes

hwmon: (ina238) Drop pointless power attribute check on attribute writes

There is only a single writeable power attribute, and it is very unlikely
that the chips supported by this driver will ever require another one.
That means checking for that attribute during runtime is unnecessary.
Drop the check. Rename the write function from ina238_write_power() to
ina238_write_power_max() to reflect that a single attribute is written.

No functional change intended.

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>