catch exceptions as const

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I873cbdcd8d4e7f553efbde0d667293d36ba5dfa4
diff --git a/src/mainapp.cpp b/src/mainapp.cpp
index 1654eca..56061d0 100644
--- a/src/mainapp.cpp
+++ b/src/mainapp.cpp
@@ -253,7 +253,7 @@
             event.run(std::nullopt);
         }
     }
-    catch (InternalFailure& e)
+    catch (const InternalFailure& e)
     {
         phosphor::logging::commit<InternalFailure>();