scsi: fcoe: fix null-ptr-deref Read in fc_release_transport

In fcoe_if_init, if fc_attach_transport(&fcoe_vport_fc_functions)
fails, need to free the previously memory and return fail, otherwise
will trigger null-ptr-deref Read in fc_release_transport.

fcoe_exit
  fcoe_if_exit
    fc_release_transport(fcoe_vport_scsi_transport)

Link: https://lore.kernel.org/r/1566279789-58207-1-git-send-email-zhengbin13@huawei.comReported-by: NHulk Robot <hulkci@huawei.com>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Signed-off-by: Nzhengbin <zhengbin13@huawei.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/fcoe/fcoe.c

@@ -1250,15 +1250,21 @@ static int __init fcoe_if_init(void)
 	/* attach to scsi transport */
 	fcoe_nport_scsi_transport =
 		fc_attach_transport(&fcoe_nport_fc_functions);
+	if (!fcoe_nport_scsi_transport)
+		goto err;
+
 	fcoe_vport_scsi_transport =
 		fc_attach_transport(&fcoe_vport_fc_functions);
-
-	if (!fcoe_nport_scsi_transport) {
-		printk(KERN_ERR "fcoe: Failed to attach to the FC transport\n");
-		return -ENODEV;
-	}
+	if (!fcoe_vport_scsi_transport)
+		goto err_vport;
 
 	return 0;
+
+err_vport:
+	fc_release_transport(fcoe_nport_scsi_transport);
+err:
+	printk(KERN_ERR "fcoe: Failed to attach to the FC transport\n");
+	return -ENODEV;
 }
 
 /**