USB: remove dead code from usb_deregister_dev()

The `name' variable is unused in usb_deregister_dev() since commit d6e5bcf4
(devfs: Remove the mode field from usb_class_driver as it's no longer needed).

Signed-off-by: Libor Pechacek <lpechacek@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>