Fix potential memory leak on failure of dsa_gen_init()

Fix potential memory leak on failure of dsa_gen_init()

When dsa_gen_set_params()  returns 0, it could have duplicated the memory for the parameter
OSSL_PKEY_PARAM_FFC_DIGEST already in gctx->mdname, leading to a memory leak.

Allocated here: https://github.com/openssl/openssl/blob/47a80fd2034cd4314d3b4958539dcd3106087109/providers/implementations/keymgmt/dsa_kmgmt.c#L524
Can return 0 here: https://github.com/openssl/openssl/blob/47a80fd2034cd4314d3b4958539dcd3106087109/providers/implementations/keymgmt/dsa_kmgmt.c#L529-L536

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/26016)