i2c: Update documentation to use .probe() again

Since commit 03c835f4 ("i2c: Switch .probe() to not take an id
parameter") .probe() is the recommended callback to implement (again).
Reflect this in the documentation and don't mention .probe_new() any
more.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>