sched: fix MC/HT scheduler optimization, without breaking the FUZZ logic.

First fix the check
	if (*imbalance + SCHED_LOAD_SCALE_FUZZ < busiest_load_per_task)
with this
	if (*imbalance < busiest_load_per_task)

As the current check is always false for nice 0 tasks (as
SCHED_LOAD_SCALE_FUZZ is same as busiest_load_per_task for nice 0
tasks).

With the above change, imbalance was getting reset to 0 in the corner
case condition, making the FUZZ logic fail. Fix it by not corrupting the
imbalance and change the imbalance, only when it finds that the HT/MC
optimization is needed.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>