machine: Add comment to abort path in machine_set_kernel_irqchip

We're not supposed to abort when the user passes a bogus value.
Since the checking is done in visit_type_OnOffSplit(), the call
to abort() is legitimate. Let's add a comment to make it
explicit.
Signed-off-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

hw/core/machine.c

@@ -65,6 +65,9 @@ static void machine_set_kernel_irqchip(Object *obj, Visitor *v,
             ms->kernel_irqchip_split = true;
             break;
         default:
+            /* The value was checked in visit_type_OnOffSplit() above. If
+             * we get here, then something is wrong in QEMU.
+             */
             abort();
         }
     }