FPII-2109: fix compile error

Change-Id: I19abf84dfccb2deb2ffd6d83ba17624b025f0718
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index f5a3ebd..331f7a2 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -742,6 +742,7 @@
 
 static void hub_init_func2(struct work_struct *ws);
 static void hub_init_func3(struct work_struct *ws);
+static void hub_release(struct kref *kref);
 
 static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
 {