scsi: ibmvscsis: Fix error return code in ibmvscsis_probe()

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

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>