chassis: Pass ec by reference

Remove passing ec by value for getProperty.

Change-Id: I9070ca7035fead14faa236eb1b17937ffe13045b
Signed-off-by: Willy Tu <wltu@google.com>
diff --git a/redfish-core/lib/chassis.hpp b/redfish-core/lib/chassis.hpp
index 8ac7caa..b27a790 100644
--- a/redfish-core/lib/chassis.hpp
+++ b/redfish-core/lib/chassis.hpp
@@ -58,7 +58,7 @@
     sdbusplus::asio::getProperty<std::vector<std::string>>(
         *crow::connections::systemBus, "xyz.openbmc_project.ObjectMapper",
         (path / "storage").str, "xyz.openbmc_project.Association", "endpoints",
-        [asyncResp](const boost::system::error_code ec,
+        [asyncResp](const boost::system::error_code& ec,
                     const std::vector<std::string>& storageList) {
         if (ec)
         {