[openssl/openssl] ebaaf3: Fix documented function return types

[bitrotlink]

  Branch: refs/heads/openssl-3.0
  Home:   https://github.com/openssl/openssl
  Commit: ebaaf357ed8c0c5b83fe19493eb4c7f27c0d3769
      https://github.com/openssl/openssl/commit/ebaaf357ed8c0c5b83fe19493eb4c7f27c0d3769
  Author: Andy Bernard <abg at bitrot.link>
  Date:   2023-03-16 (Thu, 16 Mar 2023)

  Changed paths:
    M doc/man7/provider-decoder.pod

  Log Message:
  -----------
  Fix documented function return types

The documented return type of the (incorrectly named; see below) OSSL_FUNC_decoder_export_object function signature is wrong; the correct type is int, due to the following line in core_dispatch.h:
OSSL_CORE_MAKE_FUNC(int, decoder_export_object,

Fixes #19543

Per the Github conversation with levitte and t8m for pull request #19964, the following issues are not addressed by this patch:

The macro OSSL_CORE_MAKE_FUNC in core_dispatch.h generates a function, and a corresponding function signature typedef with name ending in "_fn". The typedefed signature is unrelated to the signature of the function.
However, provider-decoder.pod describes typedefed signatures generated by the macro, but uses the names of the functions (lacking "_fn") instead of the typedefed signatures, which is a mismatch.

Also, the documented claim about OSSL_FUNC_decoder_export_object, etc that "None of these are actual functions" is contradicted by the fact that the code actually calls those functions, and calls them specifically by those names. E.g. in decoder_meth.c:
decoder->export_object = OSSL_FUNC_decoder_export_object(fns);

The functions are generated by OSSL_CORE_MAKE_FUNC.

The paragraph "None of these are actual functions"... should be replaced by something more like "These function signatures, generated by the OSSL_CORE_MAKE_FUNC macro, are for functions that are offered via function pointers in OSSL_DISPATCH arrays."

CLA: trivial

Reviewed-by: Tomas Mraz <tomas at openssl.org>
Reviewed-by: Richard Levitte <levitte at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19964)

(cherry picked from commit 04af51c276e7d785a194eb9ed199abf250c5b3b6)