IB/ipoib: Do not warn if IPoIB debugfs doesn't exist

netdev_wait_allrefs() could rebroadcast NETDEV_UNREGISTER event
multiple times until all refs are gone, which will result in calling
ipoib_delete_debug_files multiple times and printing a warning.

Remove the WARN_ONCE since checks of NULL pointers before calling
debugfs_remove are not needed.

Fixes: 771a5258 ("IB/IPoIB: ibX: failed to create mcg debug file")
Signed-off-by: Alaa Hleihel <alaa@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/ulp/ipoib/ipoib_fs.c

@@ -281,8 +281,6 @@ void ipoib_delete_debug_files(struct net_device *dev)
 {
 	struct ipoib_dev_priv *priv = ipoib_priv(dev);
 
-	WARN_ONCE(!priv->mcg_dentry, "null mcg debug file\n");
-	WARN_ONCE(!priv->path_dentry, "null path debug file\n");
 	debugfs_remove(priv->mcg_dentry);
 	debugfs_remove(priv->path_dentry);
 	priv->mcg_dentry = priv->path_dentry = NULL;