sched: Hide runqueues from direct refer at source code level

There are some points which refer the per-cpu value "runqueues" directly.
sched.c provides nice abstraction, such as cpu_rq() and this_rq(),
so we should use these macros when looking runqueues.

Signed-off-by: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
LKML-Reference: <20090617.222055.374768827975756908.mitake@dcl.info.waseda.ac.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>