[S390] qdio: continue polling if the queue is not finished

With commit c38f9608 polling was
stopped for the queue even if new data is available.

Return immediately after scheduling the queue tasklet if the queue
is not done.

Signed-off-by: Jan Glauber <jang@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>