s390/cputime: fix guest/irq/softirq times after CPU hotplug

On CPU hotplug some cpu stats contain bogus values:

$ cat /proc/stat
cpu 0 0 49 1280 0 0 0 3 0 0
cpu0 0 0 49 618 0 0 0 3 0 0
cpu1 0 0 0 662 0 0 0 0 0 0
[...]
$ echo 0 > /sys/devices/system/cpu/cpu1/online
$ echo 1 > /sys/devices/system/cpu/cpu1/online
$ cat /proc/stat
cpu 0 0 49 3200 0 450359962737 450359962737 3 0 0
cpu0 0 0 49 1956 0 0 0 3 0 0
cpu1 0 0 0 1244 0 450359962737 450359962737 0 0 0
[...]

pcpu_attach_task() needs the same assignments as vtime_task_switch.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Fixes: b7394a5f ("sched/cputime, s390: Implement delayed accounting of system time")
Cc: stable@vger.kernel.org # 4.11+
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>