iio: adc: ad7124: Refuse invalid input specifiers

iio: adc: ad7124: Refuse invalid input specifiers

The ad7124-4 has 8 analog inputs; the input select values 8 to 15 are
reserved and not to be used. These are fine for ad7124-8. For both
ad7124-4 and ad7124-8 values bigger than 15 are internal channels that
might appear as inputs in the channels specified in the device
description according to the description of commit f1794fd7bdf7 ("iio:
adc: ad7124: Remove input number limitation"), values bigger than 31
don't fit into the respective register bit field and the driver masked
them to smaller values.

Check for these invalid input specifiers and fail to probe if one is
found.

Fixes: f1794fd7bdf7 ("iio: adc: ad7124: Remove input number limitation")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://patch.msgid.link/80e3bd629d2b755ab5e061c8731dafa57d08698a.1733504533.git.u.kleine-koenig@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>