Pass boost error_code by reference

Id42ea4a90b6685a84818b87d1506c11256b3b9ae missed in couple of files

Tested: None.

Change-Id: I6cbd404132c34168cbc5901c9124ecc6ae6caacb
Signed-off-by: Lakshmi Yadlapati <lakshmiy@us.ibm.com>
diff --git a/redfish-core/lib/virtual_media.hpp b/redfish-core/lib/virtual_media.hpp
index c153f2f..73a9855 100644
--- a/redfish-core/lib/virtual_media.hpp
+++ b/redfish-core/lib/virtual_media.hpp
@@ -95,7 +95,7 @@
 {
     crow::connections::systemBus->async_method_call(
         [service, resName, aResp,
-         handler](const boost::system::error_code ec,
+         handler](const boost::system::error_code& ec,
                   const dbus::utility::ManagedObjectType& subtree) {
         if (ec)
         {