sched/fair: Fix upmigrate check in task_fits_capacity()

The upmigrate margin of a CPU is available in sched_capacity_margin_up
array not sysctl_sched_capacity_margin_up array. It is incorrectly
selected in task_fits_capacity(). Fix it.

Change-Id: Ifada3912e7d294ad30408b41edc0f4495e38e2b6
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>