s390x: css: report errors from ccw_dstream_read/write

s390x: css: report errors from ccw_dstream_read/write

ccw_dstream_read/write functions returned values are sometime
not taking into account and reported back to the upper level
of interpretation of CCW instructions.

It follows that accessing an invalid address does not trigger
a subchannel status program check to the guest as it should.

Let's test the return values of ccw_dstream_write[_buf] and
ccw_dstream_read[_buf] and report it to the caller.

Cc: qemu-stable@nongnu.org
Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
Acked-by: Halil Pasic <pasic@linux.ibm.com>
Message-Id: <1617899529-9329-2-git-send-email-pmorel@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>