ipr: Fix error return code in ipr_probe_ioa()

Fix to return error code -ENOMEM from the workqueue alloc error handling
case instead of 0, as done elsewhere in this function.

Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>
Acked-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>