fs: fix readFileSync("/proc/cpuinfo") regression

Don't use positional reads. Not all proc files support pread(), especially on
older linux kernels.

Fixes #3808.

lib/fs.js

@@ -205,12 +205,12 @@ fs.readFileSync = function(path, encoding) {
     var threw = true;
     try {
       if (size !== 0) {
-        var bytesRead = fs.readSync(fd, buffer, pos, size - pos, pos);
+        var bytesRead = fs.readSync(fd, buffer, pos, size - pos);
       } else {
         // the kernel lies about many files.
         // Go ahead and try to read some bytes.
         buffer = new Buffer(8192);
-        var bytesRead = fs.readSync(fd, buffer, 0, 8192, pos);
+        var bytesRead = fs.readSync(fd, buffer, 0, 8192);
         if (bytesRead) {
           buffers.push(buffer.slice(0, bytesRead));
         }