generate_visit_struct_fields() generates the base type's struct member
name both with and without the field prefix. Harmless, because the
field prefix is always empty there: only unboxed complex members have
a prefix, and those can't have a base type.
Clean it up anyway.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>