usb: move children to struct usb_port

usb: move children to struct usb_port

The usb_device structure contains an array of usb_device "children".
This array is only valid if the usb_device is a hub, so it makes no
sense to store it there.  Instead, store the usb_device child
in its parent usb_port structure.

Since usb_port is an internal USB core structure, add a new function to
get the USB device child, usb_hub_find_child().  Add a new macro,
usb_hub_get_each_child(), to iterate over all the children attached to a
particular USB hub.

Remove the printing the USB children array pointer from the usb-ip
driver, since it's really not necessary.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>