cpufreq: schedutil: fix check for stale utilization values

Part of the fix from commit d86ab9cf ("cpufreq: schedutil: use now
as reference when aggregating shared policy requests") is reversed in
commit 05d2ca24 ("cpufreq: schedutil: Ignore CPU load older than
WALT window size") due to a porting mistake. Restore it while keeping
the relevant change from the latter patch.

Bug: 117438867
Test: build & boot
Change-Id: I21399be760d7c8e2fff6c158368a285dc6261647
Signed-off-by: Connor O'Brien <connoro@google.com>
Signed-off-by: Alexander Winkowski <dereference23@outlook.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>