msm: lpm: check for next wake up against current time

If the next wake up time for a core is less than the
current time then we should not subtract current time
from next event time which results in a large negative
value. In case the earliest event is expired already
then do not enter cluster low power mode.

Change-Id: Iab04ef9fa4a64e76817254f9c6af4af2d80abb26
Signed-off-by: Venkat Devarasetty <vdevaras@codeaurora.org>