Fix the signature of this on 0.9.8
diff --git a/cryptography/hazmat/bindings/openssl/evp.py b/cryptography/hazmat/bindings/openssl/evp.py
index 9cd316f..0277649 100644
--- a/cryptography/hazmat/bindings/openssl/evp.py
+++ b/cryptography/hazmat/bindings/openssl/evp.py
@@ -149,7 +149,7 @@
const EVP_MD *, int, unsigned char *) = NULL;
const long Cryptography_HAS_PKEY_CTX = 0;
typedef void EVP_PKEY_CTX;
-int (*EVP_PKEY_CTX_set_signature_md)(EVP_PKEY_CTX *, EVP_MD_CTX *) = NULL;
+int (*EVP_PKEY_CTX_set_signature_md)(EVP_PKEY_CTX *, const EVP_MD *) = NULL;
int (*EVP_PKEY_sign_init)(EVP_PKEY_CTX *) = NULL;
int (*EVP_PKEY_sign)(EVP_PKEY_CTX *, unsigned char *, size_t *,
const unsigned char *, size_t) = NULL;