FROMLIST: sched/fair: Fix overutilized update in enqueue_task_fair()

enqueue_task_fair() attempts to skip the overutilized update for new
tasks as their util_avg is not accurate yet. However, the flag we check
to do so is overwritten earlier on in the function, which makes the
condition pretty much a nop.

Fix this by saving the flag early on.

Fixes: 2802bf3c ("sched/fair: Add over-utilization/tipping point
indicator")
Reported-by: Rick Yiu <rickyiu@google.com>
Bug: 173106751
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Rick Yiu <rickyiu@google.com>
Change-Id: I0a31fe4a4403fa03d1eee604adad5b6d9aff2c72