test: fix readfile-zero-byte-liar test

PR-URL: #1074
Reviewed-By: Bert Belder <[email protected]>

Author: santigimeno

test/parallel/test-fs-readfile-zero-byte-liar.js

@@ -17,7 +17,7 @@ fs.fstat = function(fd, cb) {
 };
 
 fs.fstatSync = function(fd) {
-  var st = fs._fstatSync;
+  var st = fs._fstatSync(fd);
   st.size = 0;
   return st;
 };