mfd: rn5t618: Cleanup i2c_device_id

That list was just empty, so it can be removed if .probe_new
instead of .probe is used

Suggested-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Signed-off-by: Lee Jones <lee.jones@linaro.org>