iio: adc: ad_sigma_delta: Switch to sparse friendly iio_device_claim/release_direct()

iio: adc: ad_sigma_delta: Switch to sparse friendly iio_device_claim/release_direct()

These new functions allow sparse to find failures to release
direct mode reducing chances of bugs over the claim_direct_mode()
functions that are deprecated.

This is a complex function with a lot more than the release of direct
mode to unwind on error. As such no attempt made to factor out
the inner code.

Cc: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250217141630.897334-21-jic23@kernel.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>