Convert X509_CRL* functions to use const getters

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Stephen Henson <steve@openssl.org>
diff --git a/apps/crl.c b/apps/crl.c
index abcbc45..0e8093c 100644
--- a/apps/crl.c
+++ b/apps/crl.c
@@ -250,9 +250,9 @@
     }
 
     if (badsig) {
-        ASN1_BIT_STRING *sig;
+        const ASN1_BIT_STRING *sig;
 
-        X509_CRL_get0_signature(&sig, NULL, x);
+        X509_CRL_get0_signature(x, &sig, NULL);
         corrupt_signature(sig);
     }