s390x/css: fix control flags during csch

s390x/css: fix control flags during csch

From the beginning, css support contained an error in csch handling:
instead of setting the clear bit in the function control bits twice, we
need to set the clear pending bit in the activity control bits. Let's
fix this.

Cc: qemu-stable@nongnu.org
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
(cherry picked from commit 4c6bf79a222934ac9ff0e45fc98ea1c986ed5c67)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>