sched/core: Add missing update_rq_clock() call while pushing task

rq->clock_update_flags < RQCF_ACT_SKIP warning is seen while pushing
a task from a misfit_task runqueue.

deactivate_task+0x298/0x2fc
detach_task+0x4c/0x120
active_load_balance_cpu_stop+0x254/0x580
cpu_stopper_thread+0xb8/0x13c
smpboot_thread_fn+0x1c8/0x25c
kthread+0x108/0x134
ret_from_fork+0x10/0x18

The locking of busiest_rq resets the RQCF_UPDATED flag. The code path
in active_load_balance_cpu_stop() fails to update the rq clock before
moving the 'push_task'.

Update the rq clock just before moving the push task.

Change-Id: Id0e7d7a5446775fbbbfca9fe5307240f675884e5
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>