catch exceptions as const

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ia8f2ae95679f98f2fc3f32239bbf3b3578c35888
diff --git a/extensions/phal/devtree_export.cpp b/extensions/phal/devtree_export.cpp
index 922c341..ad21332 100644
--- a/extensions/phal/devtree_export.cpp
+++ b/extensions/phal/devtree_export.cpp
@@ -23,7 +23,7 @@
         // Watch for software update
         eventRet = event.loop();
     }
-    catch (std::exception& e)
+    catch (const std::exception& e)
     {
         using namespace phosphor::logging;
         log<level::ERR>(