libct/cgroups/fs: access m.paths under lock

1. Prevent theoretical "concurrent map access" error to m.paths.

2. There is no need to call m.Paths -- we can access m.paths directly.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/fs/apply_raw.go

@@ -247,9 +247,10 @@ func (m *manager) Set(container *configs.Config) error {
 		return nil
 	}
 
-	paths := m.GetPaths()
+	m.mu.Lock()
+	defer m.mu.Unlock()
 	for _, sys := range m.getSubsystems() {
-		path := paths[sys.Name()]
+		path := m.paths[sys.Name()]
 		if err := sys.Set(path, container.Cgroups); err != nil {
 			if m.rootless && sys.Name() == "devices" {
 				continue