hwmon/pmbus: (ir38064) Expose a regulator

The chip series supported by this driver are voltage regulators, so expose
them to the regulator subsystem.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Link: https://lore.kernel.org/r/20211213142814.264802-4-arthur.heymans@9elements.com


[groeck: Added brief patch description]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>