mfd: rohm-bd718x7: Convert to i2c's .probe_new()

The probe function doesn't make use of the i2c_device_id * parameter so it
can be trivially converted.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Matti Vaittinen <mazziesaccount@gmail.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20221118224540.619276-455-uwe@kleine-koenig.org