I have the same problem, I have done the sequence bellow but nothing happens.
qm> info usb
Device 0.1, Speed 12 Mb/s, Product QEMU USB Hub
Device 0.2, Speed 12 Mb/s, Product QEMU USB Tablet
qm> info usbhost
Device 1.1, speed 480 Mb/s
Hub: USB device 0000:0000, EHCI Host Controller...