msm: rpm_resources.c: Compare sleep time with idle state overhead time

When determining an idle state to enter do not enter a state
if the sleep time is less than or equal to the overhead time
or the time needed to enter an idle state.

Change-Id: I764002b573ff39db56e69943dee85ae5959ad462
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>