Fix comment

The comment about unlocking the irq_lock was put on the wrong line.
Move it (and rephrase it a bit - the word "release" immediately after
calling an unrelated release() function - is confusing).

core/sched.cc

@@ -119,8 +119,8 @@ void cpu::do_idle()
             return;
         }
         guard.release();
-        arch::wait_for_interrupt();
-        handle_incoming_wakeups(); // auto releases irq_lock
+        arch::wait_for_interrupt(); // this unlocks irq_lock
+        handle_incoming_wakeups();
     } while (runqueue.empty());
 }