fix last warning (macro returns ASN1_ITEM_EXP *)

* 0 warnings in OpenSSL 1.0.1e
* 18 warnings in 0.9.8y
diff --git a/cryptography/hazmat/backends/openssl/asn1.py b/cryptography/hazmat/backends/openssl/asn1.py
index b56932f..a186d59 100644
--- a/cryptography/hazmat/backends/openssl/asn1.py
+++ b/cryptography/hazmat/backends/openssl/asn1.py
@@ -102,7 +102,7 @@
 
 MACROS = """
 ASN1_TIME *M_ASN1_TIME_dup(void *);
-ASN1_ITEM *ASN1_ITEM_ptr(ASN1_ITEM_EXP *);
+ASN1_ITEM_EXP *ASN1_ITEM_ptr(ASN1_ITEM_EXP *);
 
 /* These aren't macros these arguments are all const X on openssl > 1.0.x */