s390x/css: handle ccw-0 TIC correctly

In CCW-0 format TIC command 4 highest bits are ignored in the subchannel.
In CCW-1 format the TIC command 4 highest bits must be 0.
To convert TIC from CCW-0 to CCW-1 we clear the 4 highest bits
to guarantee compatibility.

Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>