sched: Reduce overestimating rq->avg_idle (based on a patch by jason low)

Date	Thu, 29 Aug 2013 13:05:34 -0700

When updating avg_idle, if the delta exceeds some max value, then avg_idle
gets set to the max, regardless of what the previous avg was. This can cause
avg_idle to often be overestimated.

This patch modifies the way we update avg_idle by always updating it with the
function call to update_avg() first. Then, if avg_idle exceeds the max, we set
it to the max.

Change-Id: I5793f6e7b33c76399b7a4caa1dec1b12994387bd
Signed-off-by: Jason Low <jason.low2@hp.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: zwliew <zhaoweiliew@gmail.com>