sched/core: Add missing update_rq_clock() in post_init_entity_util_avg()

sched/core: Add missing update_rq_clock() in post_init_entity_util_avg()

Address this rq-clock update bug:

  WARNING: CPU: 0 PID: 0 at ../kernel/sched/sched.h:797 post_init_entity_util_avg()
  rq->clock_update_flags < RQCF_ACT_SKIP

  Call Trace:
    __warn()
    post_init_entity_util_avg()
    wake_up_new_task()
    _do_fork()
    kernel_thread()
    rest_init()
    start_kernel()

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>