staging: iio: adis16240: add device to module device table

Add a of_device_id struct and MODULE_DEVICE_TABLE call, in order to add
device-tree support for this driver.

Signed-off-by: Lucas Oshiro <lucasseikioshiro@gmail.com>
Signed-off-by: Rodrigo Ribeiro <rodrigorsdc@gmail.com>
Co-developed-by: Rodrigo Ribeiro <rodrigorsdc@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>