tty: tty_ldisc: Fix an issue of code indent should use tabs

Fix an issue of code indent should use tabs, reported by checkpatch.pl.
Signed-off-by: Xiaofei Tan <tanxiaofei@huawei.com>
Link: https://lore.kernel.org/r/1617779210-51576-7-git-send-email-tanxiaofei@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>