doc/man3/ASN1_aux_cb.pod: correct return code documentation for the callbacks

doc/man3/ASN1_aux_cb.pod: correct return code documentation for the callbacks

Attempt to make the documentation match the code.

Not attempting to change what the code does at this point, it's
all very random, and since it's been there, it is effectively established
public API now.

Reviewed-by: Nikola Pajkovsky <nikolap@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.foundation>
Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Eugene Syromiatnikov <esyr@openssl.org>
MergeDate: Mon Jun 22 11:56:58 2026
(Merged from https://github.com/openssl/openssl/pull/31549)