iio: sca3000: Fix an error handling path in 'sca3000_probe()'

Use 'devm_iio_kfifo_allocate()' instead of 'iio_kfifo_allocate()' in order
to simplify code and avoid a memory leak in an error path in
'sca3000_probe()'. A call to 'sca3000_unconfigure_ring()' was missing.

Sent via the next merge window as unimportant bug and there are
other patches dependent on it.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>