catch exceptions as const

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ia6e52141afe659db8a7eaaf77fe5198028f4d173
diff --git a/phosphor-ldap-config/ldap_config.cpp b/phosphor-ldap-config/ldap_config.cpp
index 51b785a..599abaf 100644
--- a/phosphor-ldap-config/ldap_config.cpp
+++ b/phosphor-ldap-config/ldap_config.cpp
@@ -729,7 +729,7 @@
         }
         return false;
     }
-    catch (cereal::Exception& e)
+    catch (const cereal::Exception& e)
     {
         log<level::ERR>(e.what());
         std::error_code ec;