pc: don't leak a20_line

The irqs array is no longer being used
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

hw/i386/pc.c

@@ -1608,6 +1608,7 @@ void pc_basic_device_init(ISABus *isa_bus, qemu_irq *gsi,
     }
     port92 = isa_create_simple(isa_bus, "port92");
     port92_init(port92, a20_line[1]);
+    g_free(a20_line);
 
     DMA_init(isa_bus, 0);