s390/cio: fix tracepoint subchannel type field

The subchannel-type field "st" of s390_cio_stsch and s390_cio_msch
tracepoints is incorrectly filled with the subchannel-enabled SCHIB
value "ena". Fix this by assigning the correct value.

Fixes: d1de8633 ("s390 cio: Rewrite trace point class s390_class_schib")
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>