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/SB16.cpp

@@ -207,7 +207,7 @@ void SB16::dma_start(uint32_t length)
     IO::out8(0xd4, (channel % 4));
 }
 
-void SB16::handle_irq(RegisterState&)
+void SB16::handle_irq(const RegisterState&)
 {
     // Stop sound output ready for the next block.
     dsp_write(0xd5);