cpusets: Remove an unused variable

We don't use "cpu" any more after 2baab4e9 "sched: Fix
select_fallback_rq() vs cpu_active/cpu_online".

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Paul Menage <paul@paulmenage.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20120328104608.GD29022@elgon.mountain


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