usb-device-manager: Remove invalid return annotation
usb-device-manager: Remove invalid return annotation

Acked-by: Victor Toso <39b7599ff73bbf5db531748ba5250f21fa7120ff@redhat.com>

flexVDI/spice-gtk,SPICE/spice-gtk,fgouget/spice-gtk,SPICE/spice-gtk,SPICE/spice-gtk,SPICE/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk,fgouget/spice-gtk