pci: mark ROMs read-only

Looks like we didn't mark PCI ROMs as RO allowing
mischief such as guests writing there.
Further, e.g. vhost gets confused trying to allocate
enough space to log writes there. Fix it up.
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NMarcel Apfelbaum <marcel@redhat.com>
Tested-by: NLaurent Vivier <lvivier@redhat.com>

hw/pci/pci.c

@@ -2195,7 +2195,7 @@ static void pci_add_option_rom(PCIDevice *pdev, bool is_default_rom,
         snprintf(name, sizeof(name), "%s.rom", object_get_typename(OBJECT(pdev)));
     }
     pdev->has_rom = true;
-    memory_region_init_ram(&pdev->rom, OBJECT(pdev), name, size, &error_fatal);
+    memory_region_init_rom(&pdev->rom, OBJECT(pdev), name, size, &error_fatal);
     vmstate_register_ram(&pdev->rom, &pdev->qdev);
     ptr = memory_region_get_ram_ptr(&pdev->rom);
     load_image(path, ptr);