iio: magnetometer: ak8975: Relax failure on unknown id

Relax failure when driver gets an unknown device id for
allow probe for register compatible devices.

Signed-off-by: Barnabás Czémán <barnabas.czeman@mainlining.org>
Link: https://patch.msgid.link/20240819-ak09918-v4-1-f0734d14cfb9@mainlining.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>