IB: Make struct ib_uobject.id a signed int

IDR IDs are signed, so struct ib_uobject.id should be signed.  This
avoids some sparse pointer signedness warnings.
Signed-off-by: Roland Dreier <rolandd@cisco.com>

include/rdma/ib_verbs.h

@@ -730,7 +730,7 @@ struct ib_uobject {
 	struct ib_ucontext     *context;	/* associated user context */
 	void		       *object;		/* containing object */
 	struct list_head	list;		/* link to context's list */
-	u32			id;		/* index into kernel idr */
+	int			id;		/* index into kernel idr */
 	struct kref		ref;
 	struct rw_semaphore	mutex;		/* protects .live */
 	int			live;