s390/qdio: fix WARN_ON_ONCE condition

If HiperSockets Completion Queueing is enabled, qdio always
issues a warning, since the condition is always met.
This patch fixes the condition in WARN_ON_ONCE that was always
true.

Signed-off-by: Eugene Crosser <Eugene.Crosser@ru.ibm.com>
Signed-off-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>