hwmon: (pmbus) Update documentation to not use .probe_new() any more

hwmon: (pmbus) Update documentation to not use .probe_new() any more

Since commit 03c835f498b5 ("i2c: Switch .probe() to not take an id
parameter") .probe() is the recommended callback to implement an i2c
driver (again). Reflect this in the documentation and don't mention
.probe_new() which will be dropped soon.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20230627064948.593804-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>