iio: adc: ad7606: exit for invalid fdt dt_schema properties

Fix ad7606_get_chan_config() fdt parsing function to exit for error in
case of invalid dt_schema values.

Idea is to not proceed when there are values that are not allowed under
the dt_schema.

Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20250606-wip-bl-ad7606-calibration-v9-5-6e014a1f92a2@baylibre.com


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