staging: iio: resolver: ad2s1210: remove fault attribute

staging: iio: resolver: ad2s1210: remove fault attribute

Faults have been converted to events and we are now polling the fault
register each time we read a sample, so we no longer need the fault
attribute.

This attribute was not suitable for promotion out of staging anyway
since it was returning multiple values in a single attribute.

The fault clearing feature should not be needed unless we need to
support the fault output pins on the chip which is not currently
supported. So we can add this feature back in if we need it later.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20231005-ad2s1210-mainline-v4-16-ec00746840fc@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>