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/pcie_slots.hpp b/redfish-core/lib/pcie_slots.hpp
index 70efa13..42c8bb1 100644
--- a/redfish-core/lib/pcie_slots.hpp
+++ b/redfish-core/lib/pcie_slots.hpp
@@ -71,7 +71,7 @@
 
 inline void
     onPcieSlotGetAllDone(const std::shared_ptr<bmcweb::AsyncResp>& asyncResp,
-                         const boost::system::error_code ec,
+                         const boost::system::error_code& ec,
                          const dbus::utility::DBusPropertiesMap& propertiesList)
 {
     if (ec)
@@ -150,7 +150,7 @@
 inline void onMapperAssociationDone(
     const std::shared_ptr<bmcweb::AsyncResp>& asyncResp,
     const std::string& chassisID, const std::string& pcieSlotPath,
-    const std::string& connectionName, const boost::system::error_code ec,
+    const std::string& connectionName, const boost::system::error_code& ec,
     const std::variant<std::vector<std::string>>& endpoints)
 {
     if (ec)
@@ -193,7 +193,7 @@
     sdbusplus::asio::getAllProperties(
         *crow::connections::systemBus, connectionName, pcieSlotPath,
         "xyz.openbmc_project.Inventory.Item.PCIeSlot",
-        [asyncResp](const boost::system::error_code ec2,
+        [asyncResp](const boost::system::error_code& ec2,
                     const dbus::utility::DBusPropertiesMap& propertiesList) {
         onPcieSlotGetAllDone(asyncResp, ec2, propertiesList);
         });
@@ -202,7 +202,7 @@
 inline void
     onMapperSubtreeDone(const std::shared_ptr<bmcweb::AsyncResp>& asyncResp,
                         const std::string& chassisID,
-                        const boost::system::error_code ec,
+                        const boost::system::error_code& ec,
                         const dbus::utility::MapperGetSubTreeResponse& subtree)
 {
     if (ec)