krb5: krb5_enctype_to_keytype cast krb5_enctype to krb5_keytype

The struct _krb5_key_type.type is krb5_enctype.   Cast it to
krb5_keytype before assigning to the 'krb5_keytype *keytype'
output variable to avoid a warning from Clang 1500 on Darwin.

lib/krb5/crypto.c

@@ -859,7 +859,7 @@ krb5_enctype_to_keytype(krb5_context context,
     if(e == NULL) {
         return unsupported_enctype (context, etype);
     }
-    *keytype = e->keytype->type; /* XXX */
+    *keytype = (krb5_keytype)e->keytype->type;
     return 0;
 }