hwmon: (mcp3021) improve driver support for newer hwmon interface

This driver is currently broken, it does not show the in0_input sysfs
file and also returns the following message on startup:

hwmon_device_register() is deprecated. Please convert the driver to
use hwmon_device_register_with_info().

This patch converts the driver and also cleans up the 'read' function.

Signed-off-by: Marc Ferland <ferlandm@amotus.ca>
Link: https://lore.kernel.org/r/20220712193504.1374656-1-ferlandm@amotus.ca


Signed-off-by: Guenter Roeck <linux@roeck-us.net>