[SCSI] scsi_transport_iscsi: fix error return code in iscsi_transport_init()

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

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>