Make error codes take by reference

Similar to may other refactors we've done, capture
boost::system::error_code instances by const reference.

Tested: Trivial change.  Code compiles.

Change-Id: I63b6c1e3e793621cf55aca03259c2e9ffddab853
Signed-off-by: Ed Tanous <edtanous@google.com>
diff --git a/redfish-core/lib/account_service.hpp b/redfish-core/lib/account_service.hpp
index 9f3c96e..56cd492 100644
--- a/redfish-core/lib/account_service.hpp
+++ b/redfish-core/lib/account_service.hpp
@@ -2244,7 +2244,7 @@
         [asyncResp, username, password(std::move(password)),
          roleId(std::move(roleId)), enabled, newUser{std::string(*newUserName)},
          locked, userSelf, accountTypes(std::move(accountTypes))](
-            const boost::system::error_code ec, sdbusplus::message_t& m) {
+            const boost::system::error_code& ec, sdbusplus::message_t& m) {
         if (ec)
         {
             userErrorMessageHandler(m.get_error(), asyncResp, newUser,