Kernel: Use a const reference to RegisterState in IRQ handling

Author: https://github.com/supercomputer7
Commit: e880fe0765
Pull-request: https://github.com/SerenityOS/serenity/pull/1396
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/shannonbooth ✅

Kernel/Scheduler.h

@@ -49,7 +49,7 @@ extern SchedulerData* g_scheduler_data;
 class Scheduler {
 public:
     static void initialize();
-    static void timer_tick(RegisterState&);
+    static void timer_tick(const RegisterState&);
     static bool pick_next();
     static void pick_next_and_switch_now();
     static void switch_now();