[openssl/openssl] bdac6b: Clarify how to return string data

[Watson Ladd]

  Branch: refs/heads/openssl-3.0
  Home:   https://github.com/openssl/openssl
  Commit: bdac6bcc50bb93b61989cee3f74a65c34abe1bd2
      https://github.com/openssl/openssl/commit/bdac6bcc50bb93b61989cee3f74a65c34abe1bd2
  Author: Watson Ladd <watsonbladd at gmail.com>
  Date:   2023-05-25 (Thu, 25 May 2023)

  Changed paths:
    M doc/man3/OSSL_PARAM.pod

  Log Message:
  -----------
  Clarify how to return string data

Reviewed-by: Paul Dale <pauli at openssl.org>
Reviewed-by: Tomas Mraz <tomas at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21004)

(cherry picked from commit eab96453bb145cde8e447f420a4ba099a5fa7004)