usb-device-manager: mingw: win driver install callback: add missing ifdef
usb-device-manager: mingw: win driver install callback: add missing ifdef

This fixes the following compilation error message (without USE_USBREDIR):

usb-device-manager.c:183:13: error: 'spice_usb_device_manager_drv_install_cb' declared 'static' but never defined [-Werror=unused-function]

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