sched: Wrap the 'cfs_rq->nr_spread_over' field with CONFIG_SCHED_DEBUG

cfs_rq->nr_spread_over is only used when CONFIG_SCHED_DEBUG is set.
So wrap it with CONFIG_SCHED_DEBUG.

Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1304528026.15681.3.camel@localhost.localdomain


Signed-off-by: Ingo Molnar <mingo@elte.hu>