iio: adc: rockchip_saradc: add missing MODULE_* data

The module-data is currently missing. This includes the license-information
which makes the driver taint the kernel and miss symbols when compiled as
module.

Fixes: 44d6f2ef ("iio: adc: add driver for Rockchip saradc")
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>