'struct hc_driver' is not modified in this driver.

Constifying this structure moves some data to a read-only section, so
increases overall security, especially when the structure holds some
function pointers.

On a x86_64, with allmodconfig, as an example:
Before:
======
   text	   data	    bss	    dec	    hex	filename
  52065	  23176	    256	  75497	  126e9	drivers/usb/host/xen-hcd.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  52897	  22344	    256	  75497	  126e9	drivers/usb/host/xen-hcd.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
 drivers/usb/host/xen-hcd.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/host/xen-hcd.c b/drivers/usb/host/xen-hcd.c
index 1c2a95fe41e5..0a94d302911a 100644
--- a/drivers/usb/host/xen-hcd.c
+++ b/drivers/usb/host/xen-hcd.c
@@ -1388,7 +1388,7 @@ static int xenhcd_get_frame(struct usb_hcd *hcd)
 	return 0;
 }
 
-static struct hc_driver xenhcd_usb20_hc_driver = {
+static const struct hc_driver xenhcd_usb20_hc_driver = {
 	.description = "xen-hcd",
 	.product_desc = "Xen USB2.0 Virtual Host Controller",
 	.hcd_priv_size = sizeof(struct xenhcd_info),
@@ -1413,7 +1413,7 @@ static struct hc_driver xenhcd_usb20_hc_driver = {
 #endif
 };
 
-static struct hc_driver xenhcd_usb11_hc_driver = {
+static const struct hc_driver xenhcd_usb11_hc_driver = {
 	.description = "xen-hcd",
 	.product_desc = "Xen USB1.1 Virtual Host Controller",
 	.hcd_priv_size = sizeof(struct xenhcd_info),
-- 
2.51.0