iio: adc: ad7192: Remove unused member

Remove extend_name from channel macro since it is not used anywhere.

Signed-off-by: Alisa-Dariana Roman <alisa.roman@analog.com>
Link: https://lore.kernel.org/r/20231010124927.143343-3-alisadariana@gmail.com


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