mm: oom: update ulmk_kill_jiffies from oom context kill

When oc->only_positive_adj = true in a oom context kill, consider that
as ULMK kill and thus update the ulmk_kill_jiffies. This avoids the
premature OOM.

Change-Id: I11ce9161d43f6aa245356657c49959c85334d541
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>