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/Devices/KeyboardDevice.cpp

@@ -485,7 +485,7 @@ void KeyboardDevice::key_state_changed(u8 raw, bool pressed)
     m_has_e0_prefix = false;
 }
 
-void KeyboardDevice::handle_irq(RegisterState&)
+void KeyboardDevice::handle_irq(const RegisterState&)
 {
     for (;;) {
         u8 status = IO::in8(I8042_STATUS);