iio: adis16136: make use of adis lock helpers

Use the adis lib lock helpers to lock the device. This makes things
consistent with other users of the library.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20210520115909.466275-3-nuno.sa@analog.com


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