hwmon: (sch56xx) Use devres functions for watchdog

hwmon: (sch56xx) Use devres functions for watchdog

Use devm_kzalloc()/devm_watchdog_register() for
watchdog registration since it allows us to remove
the sch56xx_watchdog_data struct from the drivers
own data structs.
Remove sch56xx_watchdog_unregister since devres
takes care of that now.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20210508131457.12780-2-W_Armin@gmx.de
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
[groeck: Dropped unnecessary return; at end of void function]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>