ntb: intel: Fix error handling in intel_ntb_pci_driver_init()

A problem about ntb_hw_intel create debugfs failed is triggered with the
following log given:

 [  273.112733] Intel(R) PCI-E Non-Transparent Bridge Driver 2.0
 [  273.115342] debugfs: Directory 'ntb_hw_intel' with parent '/' already present!

The reason is that intel_ntb_pci_driver_init() returns
pci_register_driver() directly without checking its return value, if
pci_register_driver() failed, it returns without destroy the newly created
debugfs, resulting the debugfs of ntb_hw_intel can never be created later.

 intel_ntb_pci_driver_init()
   debugfs_create_dir() # create debugfs directory
   pci_register_driver()
     driver_register()
       bus_add_driver()
         priv = kzalloc(...) # OOM happened
   # return without destroy debugfs directory

Fix by removing debugfs when pci_register_driver() returns error.

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

drivers/ntb/hw/intel/ntb_hw_gen1.c

@@ -2064,12 +2064,17 @@ static struct pci_driver intel_ntb_pci_driver = {
 
 static int __init intel_ntb_pci_driver_init(void)
 {
+	int ret;
 	pr_info("%s %s\n", NTB_DESC, NTB_VER);
 
 	if (debugfs_initialized())
 		debugfs_dir = debugfs_create_dir(KBUILD_MODNAME, NULL);
 
-	return pci_register_driver(&intel_ntb_pci_driver);
+	ret = pci_register_driver(&intel_ntb_pci_driver);
+	if (ret)
+		debugfs_remove_recursive(debugfs_dir);
+
+	return ret;
 }
 module_init(intel_ntb_pci_driver_init);