ksmbd: fix unexpectedly changed path in ksmbd_vfs_kern_path_locked

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix unexpectedly changed path in ksmbd_vfs_kern_path_locked When `ksmbd_vfs_kern_path_locked` met an error and it is not the last entry, it will exit without restoring changed path buffer. But later this buffer may be used as the filename for creation.