NFSv4.1: Fix a refcounting issue in the pNFS device id cache

When we add something to the global device id cache, we need to bump the
reference count, so that the cache itself holds a reference.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/pnfs_dev.c

@@ -209,6 +209,7 @@ nfs4_insert_deviceid_node(struct nfs4_deviceid_node *new)
 
 	hlist_add_head_rcu(&new->node, &nfs4_deviceid_cache[hash]);
 	spin_unlock(&nfs4_deviceid_lock);
+	atomic_inc(&new->ref);
 
 	return new;
 }