gost_prov: OPENSSL_free what is OPENSSL_zalloc'd

  *** CID 345254:  API usage errors  (ALLOC_FREE_MISMATCH)
  /gost_prov.c: 71 in provider_ctx_new()
  65             && populate_gost_engine(ctx->e)) {
  66             ctx->core_handle = core;
  67
  68             /* Ugly hack */
  69             err_handle = ctx->proverr_handle;
  70         } else {
  >>>     CID 345254:  API usage errors  (ALLOC_FREE_MISMATCH)
  >>>     Calling "provider_ctx_free" frees "ctx" using "free" but it should have been freed using "CRYPTO_free".
  71             provider_ctx_free(ctx);
  72             ctx = NULL;
  73         }
  74         return ctx;
  75     }

Fixes: f5a3951 ("gost_prov: Avoid access to unallocated memory")
Signed-off-by: Vitaly Chikunov <vt@altlinux.org>