migration: Put zero_pages in alphabetical order

I forgot to move it when I rename it from duplicated_pages.

Message-Id: <20230504103357.22130-3-quintela@redhat.com>
Reviewed-by: David Edmondson <david.edmondson@oracle.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
1 file changed