libcutils: resolve warning in iosched_policy.c

/* libs/cutils/iosched_policy.c

/*

**

** Copyright 2007, The Android Open Source Project

** Copyright 2007-2014, The Android Open Source Project

**

** Licensed under the Apache License, Version 2.0 (the "License"); 

** you may not use this file except in compliance with the License. 

#include <cutils/iosched_policy.h>

#ifdef HAVE_ANDROID_OS

/* #include <linux/ioprio.h> */

extern int ioprio_set(int which, int who, int ioprio);

extern int ioprio_get(int which, int who);

#endif

enum {

    WHO_PROCESS = 1,