sched: change pick_next_task_fair to h_nr_running

Date	Sun, 18 Aug 2013 16:25:18 +0800

Since pick_next_task_fair only want to ensure there is some task in the
run queue to be picked up, it should use the h_nr_running instead of
nr_running, since nr_running cannot present all tasks if group existed.

Signed-off-by: Lei Wen <leiwen@marvell.com>
Signed-off-by: Paul Reioux <reioux@gmail.com>