When iomuxing is used we must not only deregister the device with stdio.c,
but also remove the reference to the device in the console_devices array
used by console-muxing. Add a call to iomux_doenv to usb_kbd_deregister to
update console_devices, which will drop the reference.

This fixes the console filling with "Failed to enqueue URB to controller"
messages after a "usb stop force", or when the USB keyboard is gone after a
"usb reset".

Signed-off-by: Hans de Goede <hdegoede@redhat.com>