staging:iio: Convert remaining drivers to module_spi_driver

Convert the IIO drivers which have not been converted yet to module_spi_driver.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
{