openssl: do not mix OpenSSL int result with CURLcode variable

[vszakats]

Seen with clang-22:

lib/vtls/openssl.c:3538:14: error: implicit conversion from 'int' to enumeration type 'CURLcode' is invalid in C++ [-Werror,-Wimplicit-int-enum-cast]
 3538 |     result = SSL_ech_set1_server_names(octx->ssl,
      |            ~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 3539 |                                        peer->origin->hostname, outername,
      |                                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 3540 |                                        0 /* do send outer */);
      |                                        ~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

Ref: https://github.com/curl/curl/actions/runs/27769068896/job/82163712258#step:42:43

Cherry-picked from #22086