When we call ssch, an interrupt might already be pending once we
return from the START SUBCHANNEL instruction. Therefore we need to
make sure interrupts are disabled until after we're done with our
processing.
Note that the subchannel lock is the same as the ccwdevice lock that
is mentioned in the documentation for ccw_device_start() and friends.
Signed-off-by: Cornelia Huck<cohuck@xxxxxxxxxx>