iio: adis: add helpers for locking

Add some helpers to lock and unlock the device. As this is such a simple
change, we update all the users that were using the lock already in this
patch.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20210218114039.216091-5-nuno.sa@analog.com


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