This most like means that the UIO driver isn’t configured to bind to the device. There are a couple of ways to do this. Easiest way is to add uio_pdrv_genirq.of_id=generic-uio to the kernel command line. If the UIO device is compiled as a module you can also add a file containing options uio_pdrv_genirq of_id=generic-uio to /etc/modprobe.d and then modprobe uio_pdrv_genirq.
Peter