catch exceptions as const

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ic8e6ade739bd5ea6e79cac6b9bb2b182748e10c8
diff --git a/extensions/openpower-pels/data_interface.hpp b/extensions/openpower-pels/data_interface.hpp
index 2469bb5..fc902a0 100644
--- a/extensions/openpower-pels/data_interface.hpp
+++ b/extensions/openpower-pels/data_interface.hpp
@@ -362,7 +362,7 @@
                 {
                     func(_hostUp);
                 }
-                catch (std::exception& e)
+                catch (const std::exception& e)
                 {
                     using namespace phosphor::logging;
                     log<level::ERR>("A host state change callback threw "