ntb: intel: Fix the NULL vs IS_ERR() bug for debugfs_create_dir()

The debugfs_create_dir() function returns error pointers.
It never returns NULL. So use IS_ERR() to check it.

Fixes: e26a5843 ("NTB: Split ntb_hw_intel and ntb_transport drivers")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

drivers/ntb/hw/intel/ntb_hw_gen1.c

@@ -778,7 +778,7 @@ static void ndev_init_debugfs(struct intel_ntb_dev *ndev)
 		ndev->debugfs_dir =
 			debugfs_create_dir(pci_name(ndev->ntb.pdev),
 					   debugfs_dir);
-		if (!ndev->debugfs_dir)
+		if (IS_ERR(ndev->debugfs_dir))
 			ndev->debugfs_info = NULL;
 		else
 			ndev->debugfs_info =