iio: imu: adis16480: initialize adis_data statically

This change overrides commit 380b107b ("iio: adis: Introduce timeouts
structure"). It removes the memory allocation and moves the 'adis_data'
information to be static on the chip_info struct.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>