fix(kernel: x86: pic): enable cascade irq

This IRQ needs to be activated for the IRQ from the slave
chip to be triggered.

kernel/arch/i686/devices/pic.c

@@ -55,6 +55,7 @@ void pic_reset()
 
     // Set and enable custom interrupts
     log_info("PIC", "Setting up custom IRQs handlers");
+    pic_enable_irq(IRQ_CASCADE); /* Allow IRQs on slave to be triggered */
     pic_enable_irq(IRQ_KEYBOARD);
     interrupts_set_handler(PIC_MASTER_VECTOR + IRQ_KEYBOARD,
                            INTERRUPT_HANDLER(irq_keyboard), NULL);