sched: EAS/WALT: fix deflated energy cost of previous CPU

WALT subtracts task util from CPU util when a task sleeps.  Therefore
at the moment of wakeup CPU util doesn't have accounted task util in
it.  Take such into consideration in order to calculate energy diff
more preciously.

Change-Id: I9bef40abb551557ebc3382ce5d77c053cfca8c1f
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>