iio: dac: ad5064: fix section mismatch in ad5064_init() in linux-next

ad5064_init() calls ad5064_spi_unregister_driver() which is annotated
__exit.

Signed-off-by: Gerard Snitselaar <dev@snitselaar.org>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>