getrusage: RUSAGE_THREAD should return ru_utime and ru_stime

Impact: task stats regression fix

Original getrusage(RUSAGE_THREAD) implementation can return ru_utime and
ru_stime. But commit "f06febc9: timers: fix itimer/many thread hang" broke it.

this patch restores it.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>