of/usb: fix build error due to of_node pointer move

Fix driver to use new location of of_node pointer (introduced by commit
use new location of of_node pointer (introduced by commit
61c7a080a5a061c976988fd4b844dfb468dda255; of: Always use 'struct
device.of_node' to get device node pointer)

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Reported-by: John Linn <john.linn@xilinx.com>
CC: Greg Kroah-Hartman <gregkh@suse.de>
CC: Alan Stern <stern@rowland.harvard.edu>
CC: linux-usb@vger.kernel.org
CC: devicetree-discuss@lists.ozlabs.org

drivers/usb/host/ehci-xilinx-of.c

@@ -151,7 +151,7 @@ static const struct hc_driver ehci_xilinx_of_hc_driver = {
 static int __devinit
 ehci_hcd_xilinx_of_probe(struct of_device *op, const struct of_device_id *match)
 {
-	struct device_node *dn = op->node;
+	struct device_node *dn = op->dev.of_node;
 	struct usb_hcd *hcd;
 	struct ehci_hcd	*ehci;
 	struct resource res;