catch exceptions as const

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ic8e6ade739bd5ea6e79cac6b9bb2b182748e10c8
diff --git a/test/openpower-pels/mocks.hpp b/test/openpower-pels/mocks.hpp
index 6d130ab..57548af 100644
--- a/test/openpower-pels/mocks.hpp
+++ b/test/openpower-pels/mocks.hpp
@@ -182,7 +182,7 @@
                 std::bind(callback, std::placeholders::_1,
                           std::placeholders::_2, std::placeholders::_3));
         }
-        catch (std::exception& e)
+        catch (const std::exception& e)
         {
             ADD_FAILURE() << "Event exception: " << e.what();
             close(fd);