s390/qeth: return proper errno on IO error

When propagating IO errors back to userspace, one error path in
qeth_irq() currently returns '1' instead of a proper errno.

Fixes: 54daaca7

 ("s390/qeth: cancel cmd on early error")
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>