spice_usb_device_manager_add_dev: use type SpiceUsbDevice for "device"
spice_usb_device_manager_add_dev: use type SpiceUsbDevice for "device"

Currently SpiceUsbDevice is a BOX for libusb_device.
In preparation for a different SpiceUsbDevice.

Renamed the libusb_device variable to libdev. Needed when
asking usbredir to check the filter.

guodong/spice-gtk,dezelin/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,Fantu/spice-gtk,mathslinux/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,guodong/spice-gtk,dezelin/spice-gtk,SPICE/spice-gtk,flexVDI/spice-gtk,mathslinux/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,SPICE/spice-gtk,elmarco/spice-gtk,Fantu/spice-gtk,elmarco/spice-gtk,SPICE/spice-gtk,dezelin/spice-gtk,guodong/spice-gtk,mathslinux/spice-gtk,dezelin/spice-gtk,elmarco/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,mathslinux/spice-gtk,fgouget/spice-gtk,Fantu/spice-gtk,elmarco/spice-gtk,SPICE/spice-gtk,fgouget/spice-gtk,Fantu/spice-gtk,guodong/spice-gtk