iio: imu: adis: create an unlocked version of adis_check_status()

This one also gets re-used in certain operations, so it makes sense to
have an unlocked version of this to group it with other
reads/writes/operations to have a single lock for the whole state change.

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