iio: adc: ad7280a: simplify with cleanup.h

Allocate the memory with scoped/cleanup.h to reduce error handling and
make the code a bit simpler.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240705-cleanup-h-iio-v1-2-77114c7e84c5@linaro.org


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