kernel/thread: Make AllWaitObjectsReady() a const qualified member function

Now that ShouldWait() is a const qualified member function, this one can
be made const qualified as well, since it can handle passing a const
qualified this pointer to ShouldWait().

src/core/hle/kernel/thread.cpp

@@ -367,7 +367,7 @@ void Thread::ChangeScheduler() {
     system.CpuCore(processor_id).PrepareReschedule();
 }
 
-bool Thread::AllWaitObjectsReady() {
+bool Thread::AllWaitObjectsReady() const {
     return std::none_of(
         wait_objects.begin(), wait_objects.end(),
         [this](const SharedPtr<WaitObject>& object) { return object->ShouldWait(this); });

src/core/hle/kernel/thread.h

@@ -299,7 +299,7 @@ public:
     }
 
     /// Determines whether all the objects this thread is waiting on are ready.
-    bool AllWaitObjectsReady();
+    bool AllWaitObjectsReady() const;
 
     const MutexWaitingThreads& GetMutexWaitingThreads() const {
         return wait_mutex_threads;