scsi: target: iscsi: Fix NULL pointer dereference in iscsi_conn_auth_required()

Fix following coccicheck error:

./drivers/target/iscsi/iscsi_target_nego.c:831:13-26: ERROR: se_nacl is NULL but dereferenced.

Link: https://lore.kernel.org/r/20220613014321.107045-1-yang.lee@linux.alibaba.com
Fixes: a75fcb09 ("scsi: target: iscsi: Extract auth functions")
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/iscsi/iscsi_target_nego.c

@@ -827,8 +827,7 @@ static bool iscsi_conn_auth_required(struct iscsit_conn *conn)
 	 */
 	se_nacl = conn->sess->se_sess->se_node_acl;
 	if (!se_nacl) {
-		pr_debug("Unknown ACL %s is trying to connect\n",
-			 se_nacl->initiatorname);
+		pr_debug("Unknown ACL is trying to connect\n");
 		return true;
 	}