hwmon: (adm9240) Convert to devm_hwmon_device_register_with_info API

Also use regmap for register caching. This change reduces code and
data size by more than 40%.

While at it, fixed some warnings reported by checkpatch.

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