hwmon: (ina238) Correctly clamp shunt voltage limit

hwmon: (ina238) Correctly clamp shunt voltage limit

When clamping a register value, the result needs to be masked against the
register size. This was missing, resulting in errors when trying to write
negative limits. Fix by masking the clamping result against the register
size.

Fixes: eacb52f010a80 ("hwmon: Driver for Texas Instruments INA238")
Cc: Nathan Rossi <nathan.rossi@digi.com>
Cc: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>