s390/cio: improve locking during cmbe allocation

During allocation of extended measurement blocks we check if the device is
already active for channel measurement and add the device to a list of
devices with active channel measurement. The check is done under ccwlock
protection and the list modification is guarded by a different lock.

To guarantee that both states are in sync make sure that both locks
are held during the allocation process (like it's already done for the
"normal" measurement block allocation).

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