sched: reduce sleep duration in wait_task_inactive()

Sleeping for a second adds unnecessary latency to hotplugging a cpu
(cpu_up). Reduce the wait time down to 1 ms which is in line with
earlier kernel versions. The 1 second value was caused due to an
incorrect merge conflict resolution during kernel upgrade.

Change-Id: Ice58147fff4d9b997def823436510ce23b02eb8e
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>