sched: walt: Fix stale walt CPU reservation flag

When CPU trying to move a task to other cpu in active load balance or
by other means, then the other helping cpu marked as reserved to avoid
 it for other scheduler decisions. Once the task moved successfully,
the reservation will be cleared enables for other scheduler decisions.
The reserved flag is been analogously protected with busy cpu’s
rq->active_balance, which is protected with runqueue locks. So whenever
rq->active_balance is set for busy cpu, then reserved flag would set for
helping cpu.

Sometimes, it is observed that, cpu is marked as reserved with no cpu's
rq->active_balance set. There are some unlikely possible corner cases
may cause this behavior:
 - On active load balance path, cpu stop machine returns queued status
   of active_balance work on cpu_stopper, which is not checked on active
   balance path. so when stop machine is not able to queue ( unlikely),
   then reserved flag wouldn't be cleared.

   So, catch the return value and on failure, clear reserved flag for cpu.

 - Clear_walt_request() called on the cpu to clear any pending walt works,
   it may possible that, push_task might have changed or cleared, then
   reserved cpu would be left uncleared.

   So clear the push_cpu independent of push_task.

Change-Id: I75d032bf399cb3da8e807186b1bc903114168a4e
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
Signed-off-by: Alexander Winkowski <dereference23@outlook.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>