qapi-visit: Fix two name arguments passed to visitors

The generated code passes mangled schema names to visit_type_enum()
and union's visit_start_struct().  Fix it to pass the names
unadulterated, like we do everywhere else.

Only qapi-schema-test.json actually has names where this makes a
difference: enum __org.qemu_x-Enum, flat union __org.qemu_x-Union2,
simple union __org.qemu_x-Union1 and its implicit enum
__org.qemu_x-Union1Kind.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>