usbcore: store each usb_device's level in the tree

This patch (as778) adds a field to struct usb_device to store the
device's level in the USB tree.  In itself this number isn't really
important.  But the overhead is very low, and in a later patch it will
be used for preventing bogus warnings from the lockdep checker.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index f5adce0..78e910b 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2414,6 +2414,7 @@
 		usb_set_device_state(udev, USB_STATE_POWERED);
 		udev->speed = USB_SPEED_UNKNOWN;
  		udev->bus_mA = hub->mA_per_port;
+		udev->level = hdev->level + 1;
 
 		/* set the address */
 		choose_address(udev);