security: plug memory leaks in transform

refs #3758

Change-Id: Id8e3aa33c76017c1662fbed9a1cafea5b39e9d6f
diff --git a/src/security/transform/block-cipher.cpp b/src/security/transform/block-cipher.cpp
index b53ec4f..327aba6 100644
--- a/src/security/transform/block-cipher.cpp
+++ b/src/security/transform/block-cipher.cpp
@@ -40,7 +40,7 @@
 
   ~Impl()
   {
-    BIO_free_all(m_sink);
+    BIO_free_all(m_cipher);
   }
 
 public: