mm: reorder oom kill logic in should_ulmk_retry()

Current implementation makes a process entered should_ulmk_retry()
after ULMK_TIMEOUT period from the previous kill, for reasons such as
high file cache which causes ignoring psi event, resulting into OOM.

Change-Id: I3d1938d3de8950256fb792471831bf012e5bdd33
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>