sched: fix typo in sched-rt-group.txt file

sched: fix typo in sched-rt-group.txt file

Fix typo about static priority's range.

    Kernel Space                     User Space
    ===============================================================
      0(high) to  98(low)     user RT priority 99(high) to 1(low)
                              with SCHED_RR or SCHED_FIFO
    ---------------------------------------------------------------
     99                       sched_priority is not used in scheduling
                              decisions(it must be specified as 0)
    ---------------------------------------------------------------
    100(high) to 139(low)     user nice -20(high) to 19(low)
    ---------------------------------------------------------------
    140                       idle task priority
    ---------------------------------------------------------------
    * ref) http://www.kernel.org/doc/man-pages/online/pages/man2/sched_setscheduler.2.html

Signed-off-by: GeunSik Lim <geunsik.lim@samsung.com>
CC: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>