scsi: iscsi: Fix reference count leak in iscsi_boot_create_kobj

kobject_init_and_add() takes reference even when it fails. If this
function returns an error, kobject_put() must be called to properly
clean up the memory associated with the object.

Link: https://lore.kernel.org/r/20200528201353.14849-1-wu000273@umn.edu


Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Qiushi Wu <wu000273@umn.edu>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>