Add missing include to functional for chef (#31404)

diff --git a/examples/chef/common/chef-fan-control-manager.cpp b/examples/chef/common/chef-fan-control-manager.cpp
index 2c42c31..3be024c 100644
--- a/examples/chef/common/chef-fan-control-manager.cpp
+++ b/examples/chef/common/chef-fan-control-manager.cpp
@@ -26,6 +26,8 @@
 #include <lib/support/CodeUtils.h>
 #include <lib/support/logging/CHIPLogging.h>
 
+#include <functional>
+
 using namespace chip;
 using namespace chip::app;
 using namespace chip::app::Clusters;