iio: core: fix memleak in iio_device_register_sysfs

When iio_device_register_sysfs_group() fails, we should
free iio_dev_opaque->chan_attr_group.attrs to prevent
potential memleak.

Fixes: 32f17172

 ("iio: core: rework iio device group creation")
Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Link: https://lore.kernel.org/r/20231208073119.29283-1-dinghao.liu@zju.edu.cn
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>