of: Add missing of_address.h to xilinx ehci driver

Build log:
In file included from drivers/usb/host/ehci-hcd.c:1208:
drivers/usb/host/ehci-xilinx-of.c: In function 'ehci_hcd_xilinx_of_probe':
drivers/usb/host/ehci-xilinx-of.c:168: error: implicit declaration of function 'of_address_to_resource'

Signed-off-by: John Williams <john.williams@petalogix.com>
Signed-off-by: Michal Simek <monstr@monstr.eu>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>