s390/qdio: don't allocate *aob array with GFP_ATOMIC

The only way to reach this allocation is via

qdio_establish()
  qdio_detect_hsicq()
    qdio_enable_async_operation()

and since qdio_establish() uses wait_event_*() just a few lines ealier,
we can trust that it certainly is never called from atomic context.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Steffen Maier <maier@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>