Make sure we also cleanse the finished key

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2259)

ssl/statem/extensions_clnt.c

diff --git a/ssl/statem/extensions_clnt.c b/ssl/statem/extensions_clnt.c
index 04dbea1..eb8cfa3 100644
--- a/ssl/statem/extensions_clnt.c
+++ b/ssl/statem/extensions_clnt.c
@@ -820,6 +820,7 @@
     ret = 1;
  err:
     OPENSSL_cleanse(binderkey, sizeof(binderkey));
+    OPENSSL_cleanse(finishedkey, sizeof(finishedkey));
     EVP_PKEY_free(mackey);
     EVP_MD_CTX_free(mctx);