xhci: dbgtty: Fix unregister on tty_alloc_driver() failure

commit 25b8dfc upstream.

Make sure to set dbc_tty_driver to NULL to match the check in
dbc_tty_exit(). For that, make detached error handling path common to the
other branch in the same function.

Fixes: 4521f16 ("xhci: dbctty: split dbc tty driver registration and unregistration functions.")
Cc: stable@vger.kernel.org # v5.10
Cc: Mathias Nyman <mathias.nyman@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Lucas De Marchi <ldemarchi@nvidia.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://patch.msgid.link/20260806142113.2436238-9-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: lucasdemarchi

drivers/usb/host/xhci-dbgtty.c

@@ -628,8 +628,8 @@ int dbc_tty_init(void)
 	dbc_tty_driver = tty_alloc_driver(64, TTY_DRIVER_REAL_RAW |
 					  TTY_DRIVER_DYNAMIC_DEV);
 	if (IS_ERR(dbc_tty_driver)) {
-		idr_destroy(&dbc_tty_minors);
-		return PTR_ERR(dbc_tty_driver);
+		ret = PTR_ERR(dbc_tty_driver);
+		goto fail;
 	}
 
 	dbc_tty_driver->driver_name = "dbc_serial";
@@ -649,11 +649,17 @@ int dbc_tty_init(void)
 	ret = tty_register_driver(dbc_tty_driver);
 	if (ret) {
 		pr_err("Can't register dbc tty driver\n");
-		tty_driver_kref_put(dbc_tty_driver);
-		idr_destroy(&dbc_tty_minors);
-		dbc_tty_driver = NULL;
+		goto fail_put;
 	}
 
+	return ret;
+
+fail_put:
+	tty_driver_kref_put(dbc_tty_driver);
+fail:
+	idr_destroy(&dbc_tty_minors);
+	dbc_tty_driver = NULL;
+
 	return ret;
 }