xen/usb: switch xen-hcd to use INVALID_GRANT_REF

Instead of using a private macro for an invalid grant reference use
the common one.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juergen Gross <jgross@suse.com>

drivers/usb/host/xen-hcd.c

@@ -87,8 +87,6 @@ struct xenhcd_info {
 	bool error;
 };
 
-#define GRANT_INVALID_REF 0
-
 #define XENHCD_RING_JIFFIES (HZ/200)
 #define XENHCD_SCAN_JIFFIES 1
 
@@ -1100,17 +1098,17 @@ static void xenhcd_destroy_rings(struct xenhcd_info *info)
 		unbind_from_irqhandler(info->irq, info);
 	info->irq = 0;
 
-	if (info->urb_ring_ref != GRANT_INVALID_REF) {
+	if (info->urb_ring_ref != INVALID_GRANT_REF) {
 		gnttab_end_foreign_access(info->urb_ring_ref,
 					  (unsigned long)info->urb_ring.sring);
-		info->urb_ring_ref = GRANT_INVALID_REF;
+		info->urb_ring_ref = INVALID_GRANT_REF;
 	}
 	info->urb_ring.sring = NULL;
 
-	if (info->conn_ring_ref != GRANT_INVALID_REF) {
+	if (info->conn_ring_ref != INVALID_GRANT_REF) {
 		gnttab_end_foreign_access(info->conn_ring_ref,
 					  (unsigned long)info->conn_ring.sring);
-		info->conn_ring_ref = GRANT_INVALID_REF;
+		info->conn_ring_ref = INVALID_GRANT_REF;
 	}
 	info->conn_ring.sring = NULL;
 }
@@ -1123,8 +1121,8 @@ static int xenhcd_setup_rings(struct xenbus_device *dev,
 	grant_ref_t gref;
 	int err;
 
-	info->urb_ring_ref = GRANT_INVALID_REF;
+	info->urb_ring_ref = INVALID_GRANT_REF;
-	info->conn_ring_ref = GRANT_INVALID_REF;
+	info->conn_ring_ref = INVALID_GRANT_REF;
 
 	urb_sring = (struct xenusb_urb_sring *)get_zeroed_page(
 							GFP_NOIO | __GFP_HIGH);