Update openssl.c
diff --git a/lib/openssl.c b/lib/openssl.c
index 16f4f9e..53b6dcc 100644
--- a/lib/openssl.c
+++ b/lib/openssl.c
@@ -1091,7 +1091,7 @@
     } break;
 #if defined EVP_PKEY_ED25519
     case EVP_PKEY_ED25519:
-        PUSH_SCHEME(PTLS_SIGNATURE_ED25519, EVP_sha512());
+        PUSH_SCHEME(PTLS_SIGNATURE_ED25519, NULL);
         break;
 #endif
     default: