iio: sca3000: Handle errors returned by 'sca3000_configure_ring()' in 'sca3000_probe()'

'sca3000_configure_ring()' can fail, so test its return value and
propagate it if needed.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>