ocfs2: Proper cleanup in case of error in ocfs2_register_hb_callbacks()

If ocfs2_register_hb_callbacks() succeeds on its first callback but fails
its second, it doesn't release the first on the way out. Fix that.

While we're at it, o2hb_unregister_callback() never returns anything but
0, so let's make it void.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

fs/ocfs2/cluster/heartbeat.h

@@ -70,7 +70,7 @@ void o2hb_setup_callback(struct o2hb_callback_func *hc,
 			 void *data,
 			 int priority);
 int o2hb_register_callback(struct o2hb_callback_func *hc);
-int o2hb_unregister_callback(struct o2hb_callback_func *hc);
+void o2hb_unregister_callback(struct o2hb_callback_func *hc);
 void o2hb_fill_node_map(unsigned long *map,
 			unsigned bytes);
 void o2hb_init(void);