s390/qdio: reduce access to cdev->private->qdio_data

Remove all usage of cdev->private->qdio_data that's buried deep in
internal code. This should only be used by the exported driver API,
which can then pass around a proper qdio_irq pointer.

Also trivially merge some initializations with their definitions.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>