Apply PyObject.patch correcting the return type of several functions

Author: wsanchez
Reviewer: exarkun
Fixes: #2018311

diff --git a/src/crypto/crypto.c b/src/crypto/crypto.c
index d4fc882..d239a3b 100644
--- a/src/crypto/crypto.c
+++ b/src/crypto/crypto.c
@@ -592,7 +592,7 @@
     if (py_pkey) {
 	py_pkey->initialized = 0;
     }
-    return py_pkey;
+    return (PyObject *)py_pkey;
 }
 
 static char crypto_X509Extension_doc[] = "\n\