Take boost error_code by reference

By convention, we should be following boost here, and passing error_code
by reference, not by value.  This makes our code consistent, and removes
the need for a copy in some cases.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: Id42ea4a90b6685a84818b87d1506c11256b3b9ae
diff --git a/redfish-core/lib/cable.hpp b/redfish-core/lib/cable.hpp
index 0fc36b4..423ea9d 100644
--- a/redfish-core/lib/cable.hpp
+++ b/redfish-core/lib/cable.hpp
@@ -24,7 +24,7 @@
  */
 inline void
     fillCableProperties(crow::Response& resp,
-                        const boost::system::error_code ec,
+                        const boost::system::error_code& ec,
                         const dbus::utility::DBusPropertiesMap& properties)
 {
     if (ec)
@@ -97,7 +97,7 @@
                 *crow::connections::systemBus, service, cableObjectPath,
                 interface,
                 [asyncResp](
-                    const boost::system::error_code ec,
+                    const boost::system::error_code& ec,
                     const dbus::utility::DBusPropertiesMap& properties) {
                 fillCableProperties(asyncResp->res, ec, properties);
                 });