msm: kgsl: Correct the initial idle_timer value

The gpu idle_timer initial value is incorrect in the DT for 8974

Change-Id: I07cd42c93070162bf520cfc9cfa7e15a46b2c2e8
Signed-off-by: Vladimir Razgulin <vrazguli@codeaurora.org>
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>