iio_readdev corrupts the data when using auto detection 

Run iio_readdev in the auto detection mode (i.e. "-a"):

```
#: ./iio_readdev -a -s 2 cf-ad9361-lpc
Using auto-detected IIO context at URI "usb:20.10.5"
??????%
```

All data produced to stdout. Thus the message "Using auto-detected IIO context at URI "usb:20.10.5"" corrupts the output.