SUNRPC: remove BUG_ON in rpc_put_sb_net

Replace BUG_ON() with WARN_ON() - the condition is definitely a misuse
of the API, but shouldn't cause a crash.
Signed-off-by: Weston Andros Adamson <dros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/rpc_pipe.c

@@ -1093,7 +1093,7 @@ void rpc_put_sb_net(const struct net *net)
 {
 	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
 
-	BUG_ON(sn->pipefs_sb == NULL);
+	WARN_ON(sn->pipefs_sb == NULL);
 	mutex_unlock(&sn->pipefs_sb_lock);
 }
 EXPORT_SYMBOL_GPL(rpc_put_sb_net);