sched/prio: Use DEFAULT_PRIO to define NICE_TO_PRIO() and PRIO_TO_NICE()

There is already a macro named DEFAULT_PRIO in prio.h, we can use it
to define NICE_TO_PRIO and PRIO_TO_NICE rather than use hard coding
of (MAX_RT_PRIO + 20).
Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/4e28ec36fb49e8906027cbbdd900ab26a149905e.1392103744.git.yangds.fnst@cn.fujitsu.comSigned-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/sched/prio.h

@@ -25,8 +25,8 @@
  * to static priority [ MAX_RT_PRIO..MAX_PRIO-1 ],
  * and back.
  */
-#define NICE_TO_PRIO(nice)	(MAX_RT_PRIO + (nice) + 20)
-#define PRIO_TO_NICE(prio)	((prio) - MAX_RT_PRIO - 20)
+#define NICE_TO_PRIO(nice)	((nice) + DEFAULT_PRIO)
+#define PRIO_TO_NICE(prio)	((prio) - DEFAULT_PRIO)
 
 /*
  * 'User priority' is the nice value converted to something we