iio_adi_xflow_check 'failed to read status register'

I'm using an ad7768 with the ad7768evb reference design in the adi-hdl repo on a zedboard.

I;ve been having trouble with dropped data, so I decided to run `iio_adi_xflow_check`.  But I get the following:

# iio_adi_xflow_check --uri local: -s65536 iio:device1
Monitoring ad7768 for underflows/overflows
Failed to read status register: No such file or directory
Failed to read status register: No such file or directory
Failed to read status register: No such file or directory