USB: core: fix device node leak

Make sure to release any OF device-node reference taken when creating
the USB device.

Note that we currently do not hold a reference to the root hub
device-tree node (i.e. the parent controller node).

Fixes: 69bec725 ("USB: core: let USB device know device node")
Cc: stable <stable@vger.kernel.org>	# v4.6
Acked-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>