sched: minor optimizations in wake_affine and select_task_rq_fair

This patch does following:
o Removes unused variable and argument "rq".
o Optimizes one of the "if" conditions in wake_affine() - i.e.  if
  "balanced" is true, we need not do rest of the calculations in the
  condition.
o If this cpu is same as the previous cpu (on which woken up task
  was running when it went to sleep), no need to call wake_affine at all.

Signed-off-by: Amit K Arora <aarora@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>