sched: don't call task_group() many times in set_task_rq()

It improves perfomance, especially if autogroup enabled.

The size of set_task_rq() was 0x180 and now it is 0xa0.

Signed-off-by: Andrew Vagin <avagin@openvz.org>
Signed-off-by: artas182x <artas182x@gmail.com>
Voltage update for more stability