s390/qdio: clean up qdio_check_outbound_after_thinint()

This helper is not thinint-specific, qdio_get_next_buffers() also calls it
for non-thinint devices. So give it a more fitting name, and while at it
adjust its parameter.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>