rapidio: fix possible UAF when kfifo_alloc() fails

If kfifo_alloc() fails in mport_cdev_open(), goto err_fifo and just free
priv. But priv is still in the chdev->file_list, then list traversal
may cause UAF. This fixes the following smatch warning:

drivers/rapidio/devices/rio_mport_cdev.c:1930 mport_cdev_open() warn: '&priv->list' not removed from list

Link: https://lkml.kernel.org/r/20221123095147.52408-1-wangweiyang2@huawei.com
Fixes: e8de370188 ("rapidio: add mport char device driver")
Signed-off-by: Wang Weiyang <wangweiyang2@huawei.com>
Cc: Alexandre Bounine <alex.bou9@gmail.com>
Cc: Dan Carpenter <error27@gmail.com>
Cc: Jakob Koschel <jakobkoschel@gmail.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/rapidio/devices/rio_mport_cdev.c

@@ -1904,10 +1904,6 @@ static int mport_cdev_open(struct inode *inode, struct file *filp)
 
 	priv->md = chdev;
 
-	mutex_lock(&chdev->file_mutex);
-	list_add_tail(&priv->list, &chdev->file_list);
-	mutex_unlock(&chdev->file_mutex);
-
 	INIT_LIST_HEAD(&priv->db_filters);
 	INIT_LIST_HEAD(&priv->pw_filters);
 	spin_lock_init(&priv->fifo_lock);
@@ -1926,6 +1922,9 @@ static int mport_cdev_open(struct inode *inode, struct file *filp)
 	spin_lock_init(&priv->req_lock);
 	mutex_init(&priv->dma_lock);
 #endif
+	mutex_lock(&chdev->file_mutex);
+	list_add_tail(&priv->list, &chdev->file_list);
+	mutex_unlock(&chdev->file_mutex);
 
 	filp->private_data = priv;
 	goto out;