staging: speakup: remove unused code

In spk_ttyio_release we read tty's index but never do anything with it.
The patch removes this dead code.

Signed-off-by: Okash Khawaja <okash.khawaja@gmail.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>