iio: potentiometer: max5487: Don't return an error in .remove()

The only effect of returning an error in an spi .remove() callback is
that the spi core issues a generic warning message. Instead emit a more
specific error message and return 0 to not report the same issue twice.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Link: https://lore.kernel.org/r/20211013203223.2694577-15-u.kleine-koenig@pengutronix.de


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