sched: Drop the need_resched() loop from cond_resched()

The schedule() function is a loop that reschedules the current
task while the TIF_NEED_RESCHED flag is set:

void schedule(void)
{
need_resched:
	/* schedule code */
	if (need_resched())
		goto need_resched;
}

And cond_resched() repeat this loop:

do {
	add_preempt_count(PREEMPT_ACTIVE);
	schedule();
	sub_preempt_count(PREEMPT_ACTIVE);
} while(need_resched());

This loop is needless because schedule() already did the check
and nothing can set TIF_NEED_RESCHED between schedule() exit
and the loop check in need_resched().

Then remove this needless loop.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1247725694-6082-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>