staging: speakup: migrate bns to tty

Migration of bns was missed out in the patch
https://patchwork.kernel.org/patch/9727725/. This patch does it by
updating relevant function pointers, just like in the patch linked
above.
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>

drivers/staging/speakup/speakup_bns.c

@@ -96,10 +96,10 @@ static struct spk_synth synth_bns = {
 	.startup = SYNTH_START,
 	.checkval = SYNTH_CHECK,
 	.vars = vars,
-	.io_ops = &spk_serial_io_ops,
-	.probe = spk_serial_synth_probe,
-	.release = spk_serial_release,
-	.synth_immediate = spk_serial_synth_immediate,
+	.io_ops = &spk_ttyio_ops,
+	.probe = spk_ttyio_synth_probe,
+	.release = spk_ttyio_release,
+	.synth_immediate = spk_ttyio_synth_immediate,
 	.catch_up = spk_do_catch_up,
 	.flush = spk_synth_flush,
 	.is_alive = spk_synth_is_alive_restart,