TTY: include termios.h in tty_driver.h

We reference termios and termiox in tty_driver.h, but we do not include
linux/termios.h where these are defined. Add the #include properly.

Otherwise when we include tty_driver.h, we get compile errors.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Greg KH <gregkh@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>