s390: remove superfluous tpi from wait_cons_dev

wait_cons_dev waits for a particular subchannel to complete an I/O.
It is not necessary to use tpi to get the subchannel id as it is
already known. This avoids changes to the interrupt subclass mask
and allows to remove the lock & unlock of the subchannel lock.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>