backlight: ktz8866: 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>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230127152639.1347229-1-u.kleine-koenig@pengutronix.de