sched/fair: Fix previous CPU util calculation in cpu_util_next_walt()

When a task is waking and both evaluation CPU and the destination
CPU are the task's previous CPU, the task utilization must be
added to the evaluation CPU's utilization. But it is not done.
Due to this the task may get placed on the previous CPU incorrectly
and results in suboptimal power and performance.

Change-Id: I62b5eec3046b7fef31321125dd76f67afe8f567d
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>