hw/isa/i82378: Remove unused "io" attribute

The attribute isn't used since commit 5c9736789b79ea49cd236ac326f0a414f63b1015
"i82378: Cleanup implementation".

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-Id: <20230523195608.125820-4-shentey@gmail.com>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>

hw/isa/i82378.c

@@ -34,7 +34,6 @@ struct I82378State {
 
     qemu_irq cpu_intr;
     qemu_irq *isa_irqs_in;
-    MemoryRegion io;
 };
 
 static const VMStateDescription vmstate_i82378 = {