s390/early: use system_ctl_set_bit() instead of local_ctl_set_bit()

s390/early: use system_ctl_set_bit() instead of local_ctl_set_bit()

Use system_ctl_set_bit() instead of local_ctl_set_bit() to reflect
that the control register changes are supposed to be global. This
change is just for documentation purposes, since it still results only
in local control register contents being changed.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>