iio: adis: Drop non Managed device functions

Drop `adis_setup_buffer_and_trigger()`. All users were updated to use
the devm version of this function. This avoids having almost the same
code repeated.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20200915120258.161587-11-nuno.sa@analog.com


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