target: fix regression with dev_link_magic in target_fabric_port_link

This is to fix a regression that only affect the stable (not for the mainline)
that the stable commit fdf9d862 was incorrectly placed dev->dev_link_magic check
before the *dev assignment in target_fabric_port_link() due to fuzzy automatically
context adjustment during the back-porting.
Reported-by: Chris Boot <bootc@bootc.net>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: CAI Qian <caiqian@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/target/target_core_fabric_configfs.c

@@ -752,12 +752,6 @@ static int target_fabric_port_link(
 	struct target_fabric_configfs *tf;
 	int ret;
 
-	if (dev->dev_link_magic != SE_DEV_LINK_MAGIC) {
-		pr_err("Bad dev->dev_link_magic, not a valid se_dev_ci pointer:"
-			" %p to struct se_device: %p\n", se_dev_ci, dev);
-		return -EFAULT;
-	}
-
 	tpg_ci = &lun_ci->ci_parent->ci_group->cg_item;
 	se_tpg = container_of(to_config_group(tpg_ci),
 				struct se_portal_group, tpg_group);
@@ -775,6 +769,11 @@ static int target_fabric_port_link(
 		ret = -ENODEV;
 		goto out;
 	}
+	if (dev->dev_link_magic != SE_DEV_LINK_MAGIC) {
+		pr_err("Bad dev->dev_link_magic, not a valid se_dev_ci pointer:"
+			" %p to struct se_device: %p\n", se_dev_ci, dev);
+		return -EFAULT;
+	}
 
 	lun_p = core_dev_add_lun(se_tpg, dev->se_hba, dev,
 				lun->unpacked_lun);