net/mlx5: Don't fail driver on failure to create debugfs

Clang warns:

drivers/net/ethernet/mellanox/mlx5/core/main.c:1278:6: warning: variable
'err' is used uninitialized whenever 'if' condition is true
[-Wsometimes-uninitialized]
        if (!priv->dbg_root) {
            ^~~~~~~~~~~~~~~
drivers/net/ethernet/mellanox/mlx5/core/main.c:1303:9: note:
uninitialized use occurs here
        return err;
               ^~~
drivers/net/ethernet/mellanox/mlx5/core/main.c:1278:2: note: remove the
'if' if its condition is always false
        if (!priv->dbg_root) {
        ^~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/mellanox/mlx5/core/main.c:1259:9: note: initialize
the variable 'err' to silence this warning
        int err;
               ^
                = 0
1 warning generated.

The check of returned value of debugfs_create_dir() is wrong because
by the design debugfs failures should never fail the driver and the
check itself was wrong too. The kernel compiled without CONFIG_DEBUG_FS
will return ERR_PTR(-ENODEV) and not NULL as expected.

Fixes: 11f3b84 ("net/mlx5: Split mdev init and pci init")
Link: ClangBuiltLinux#1042
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/net/ethernet/mellanox/mlx5/core/main.c

@@ -1281,11 +1281,6 @@ static int mlx5_mdev_init(struct mlx5_core_dev *dev, int profile_idx)
 
 	priv->dbg_root = debugfs_create_dir(dev_name(dev->device),
 					    mlx5_debugfs_root);
-	if (!priv->dbg_root) {
-		dev_err(dev->device, "mlx5_core: error, Cannot create debugfs dir, aborting\n");
-		goto err_dbg_root;
-	}
-
 	err = mlx5_health_init(dev);
 	if (err)
 		goto err_health_init;
@@ -1300,7 +1295,6 @@ static int mlx5_mdev_init(struct mlx5_core_dev *dev, int profile_idx)
 	mlx5_health_cleanup(dev);
 err_health_init:
 	debugfs_remove(dev->priv.dbg_root);
-err_dbg_root:
 	mutex_destroy(&priv->pgdir_mutex);
 	mutex_destroy(&priv->alloc_mutex);
 	mutex_destroy(&priv->bfregs.wc_head.lock);