tty: vt, return error when con_startup fails

commit 6798df4c upstream.

When csw->con_startup() fails in do_register_con_driver, we return no
error (i.e. 0). This was changed back in 2006 by commit 3e795de7.
Before that we used to return -ENODEV.

So fix the return value to be -ENODEV in that case again.

Fixes: 3e795de7 ("VT binding: Add binding/unbinding support for the VT console")
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Reported-by: "Dan Carpenter" <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>

drivers/tty/vt/vt.c

@@ -3534,9 +3534,10 @@ static int do_register_con_driver(const struct consw *csw, int first, int last)
 		goto err;
 
 	desc = csw->con_startup();
-
-	if (!desc)
+	if (!desc) {
+		retval = -ENODEV;
 		goto err;
+	}
 
 	retval = -EINVAL;