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.hpp b/redfish-core/lib/pcie.hpp
index 5332a39..c3b7546 100644
--- a/redfish-core/lib/pcie.hpp
+++ b/redfish-core/lib/pcie.hpp
@@ -169,7 +169,7 @@
 
         auto getPCIeDeviceCallback =
             [asyncResp, device](
-                const boost::system::error_code ec,
+                const boost::system::error_code& ec,
                 const dbus::utility::DBusPropertiesMap& pcieDevProperties) {
             if (ec)
             {
@@ -288,7 +288,7 @@
 
         auto getPCIeDeviceCallback =
             [asyncResp, device](
-                const boost::system::error_code ec,
+                const boost::system::error_code& ec,
                 const dbus::utility::DBusPropertiesMap& pcieDevProperties) {
             if (ec)
             {
@@ -364,7 +364,7 @@
         }
         auto getPCIeDeviceCallback =
             [asyncResp, device, function](
-                const boost::system::error_code ec,
+                const boost::system::error_code& ec,
                 const dbus::utility::DBusPropertiesMap& pcieDevProperties) {
             if (ec)
             {