Update code in part2_3_events

Update the code block in tutorial post event-driven-programming from
passing by pointer to passing by reference.

Jira: https://gem5.atlassian.net/browse/GEM5-1331
Change-Id: I409d8b04d4a79c22b08905f68fdef10c8243dd86
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/72198
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
diff --git a/_pages/documentation/learning_gem5/part2/part2_3_events.md b/_pages/documentation/learning_gem5/part2/part2_3_events.md
index 6059ce6..9817d3d 100644
--- a/_pages/documentation/learning_gem5/part2/part2_3_events.md
+++ b/_pages/documentation/learning_gem5/part2/part2_3_events.md
@@ -42,7 +42,7 @@
     EventFunctionWrapper event;
 
   public:
-    HelloObject(HelloObjectParams *p);
+    HelloObject(const HelloObjectParams &p);
 
     void startup();
 };
@@ -61,7 +61,7 @@
 so we can call member functions of the instance of the class.
 
 ```cpp
-HelloObject::HelloObject(HelloObjectParams *params) :
+HelloObject::HelloObject(const HelloObjectParams &params) :
     SimObject(params), event([this]{processEvent();}, name())
 {
     DPRINTF(HelloExample, "Created the hello object\n");
@@ -158,7 +158,7 @@
 `timesLeft`.
 
 ```cpp
-HelloObject::HelloObject(HelloObjectParams *params) :
+HelloObject::HelloObject(const HelloObjectParams &params) :
     SimObject(params), event([this]{processEvent();}, name()),
     latency(100), timesLeft(10)
 {