USB: fix __must_check warnings in drivers/usb/core/

Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/core/usb.h b/drivers/usb/core/usb.h
index e8bc2e4..0c09ecc 100644
--- a/drivers/usb/core/usb.h
+++ b/drivers/usb/core/usb.h
@@ -1,10 +1,10 @@
 /* Functions local to drivers/usb/core/ */
 
-extern void usb_create_sysfs_dev_files (struct usb_device *dev);
+extern int usb_create_sysfs_dev_files (struct usb_device *dev);
 extern void usb_remove_sysfs_dev_files (struct usb_device *dev);
-extern void usb_create_sysfs_intf_files (struct usb_interface *intf);
+extern int usb_create_sysfs_intf_files (struct usb_interface *intf);
 extern void usb_remove_sysfs_intf_files (struct usb_interface *intf);
-extern void usb_create_ep_files(struct device *parent, struct usb_host_endpoint *endpoint,
+extern int usb_create_ep_files(struct device *parent, struct usb_host_endpoint *endpoint,
 				struct usb_device *udev);
 extern void usb_remove_ep_files(struct usb_host_endpoint *endpoint);