usb: core: move root hub's device node assignment after it is added to bus

usb: core: move root hub's device node assignment after it is added to bus

When the root hub device is added to the bus, it tries to get pins
information from pinctrl (see pinctrl_bind_pins, at really_probe), if
the pin information is described at DT, it will show below error since
the root hub's device node is the same with controller's, but controller's
pin has already been requested when it is added to platform bus.

	imx6q-pinctrl 20e0000.iomuxc: pin MX6Q_PAD_GPIO_1 already
       	requested by 2184000.usb; cannot claim for usb1
	imx6q-pinctrl 20e0000.iomuxc: pin-137 (usb1) status -22
	imx6q-pinctrl 20e0000.iomuxc: could not request pin 137
       	(MX6Q_PAD_GPIO_1) from group usbotggrp-3 on device 20e0000.iomuxc
	usb usb1: Error applying setting, reverse things back

To fix this issue, we move the root hub's device node assignment (equals
to contrller's) after device is added to bus, we only need to know root
hub's device node information after the device under root hub is created,
so this movement will not affect current function.

Signed-off-by: Peter Chen <peter.chen@nxp.com>
Reported-by: Lars Steubesand <lars.steubesand@philips.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>