sched/fair: Remove 'cpu_busy' parameter from update_next_balance()

The update_next_balance() function is only used by idle balancing, so its
'cpu_busy' parameter is always 0.

Open code it instead of passing it around.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1470378689-14892-1-git-send-email-leo.yan@linaro.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>