catch exceptions as const

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: If708716cc4c05ad30ea0fcd89518236d815bdafb
diff --git a/example/asio-example.cpp b/example/asio-example.cpp
index b1e1132..317deb5 100644
--- a/example/asio-example.cpp
+++ b/example/asio-example.cpp
@@ -288,7 +288,7 @@
             message intMsg = conn->call(readyMsg);
             intMsg.read(ready);
         }
-        catch (sdbusplus::exception::SdBusError& e)
+        catch (const sdbusplus::exception::SdBusError& e)
         {
             ready = 0;
             // pause to give the server a chance to start up