s390/cio: fix memleak in channel measurement

The measurement block for the extended measurement data is not freed when
switching off per device measurement. Free the measurement block after HW
stopped accessing it.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>