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

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.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>