USB host: make Open Firmware device id constant

The match_table field of the struct of_device_id is constant in <linux/of_platform.h>
so it is worth to make the initialization data also constant.

The semantic match that finds this kind of pattern is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@r@
disable decl_init,const_decl_init;
identifier I1, I2, x;
@@
	struct I1 {
	  ...
	  const struct I2 *x;
	  ...
	};
@s@
identifier r.I1, y;
identifier r.x, E;
@@
	struct I1 y = {
	  .x = E,
	};
@c@
identifier r.I2;
identifier s.E;
@@
	const struct I2 E[] = ... ;
@depends on !c@
identifier r.I2;
identifier s.E;
@@
+	const
	struct I2 E[] = ...;
// </smpl>

Signed-off-by: Németh Márton <nm127@freemail.hu>
Cc: Julia Lawall <julia@diku.dk>
Cc: cocci@diku.dk
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

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

@@ -281,7 +281,7 @@ static int ehci_hcd_xilinx_of_shutdown(struct of_device *op)
 }
 
 
-static struct of_device_id ehci_hcd_xilinx_of_match[] = {
+static const struct of_device_id ehci_hcd_xilinx_of_match[] = {
 		{.compatible = "xlnx,xps-usb-host-1.00.a",},
 	{},
 };