usb, gadget: use appropriate warning accessors

Use the appropriate WARN() and WARN_ON() accessors to avoid a build error
when CONFIG_BUG=n:

	drivers/usb/gadget/configfs.c: In function 'config_usb_cfg_unlink':
	drivers/usb/gadget/configfs.c:442:2: error: implicit declaration of function '__WARN_printf'
	drivers/usb/gadget/configfs.c: In function 'configfs_do_nothing':
	drivers/usb/gadget/configfs.c:733:2: error: implicit declaration of function '__WARN'
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/configfs.c

@@ -439,7 +439,7 @@ static int config_usb_cfg_unlink(
 		}
 	}
 	mutex_unlock(&gi->lock);
-	__WARN_printf("Unable to locate function to unbind\n");
+	WARN(1, "Unable to locate function to unbind\n");
 	return 0;
 }
 
@@ -730,7 +730,7 @@ USB_CONFIG_STRINGS_LANG(gadget_strings, gadget_info);
 
 static int configfs_do_nothing(struct usb_composite_dev *cdev)
 {
-	__WARN();
+	WARN_ON(1);
 	return -EINVAL;
 }