backlight: lp855x: Convert to i2c's .probe_new()

.probe_new() doesn't get the i2c_device_id * parameter, so determine
that explicitly in the probe function.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20221118224540.619276-592-uwe@kleine-koenig.org