tty: Fix whitespace inconsistencies in vt_io_ioctl

Replaces spaces with tabs for indentation.
Signed-off-by: Yan.Gao <gao.yanB@h3c.com>
Link: https://lore.kernel.org/r/20201209030551.48029-1-gao.yanB@h3c.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>