[patch] staging: speakup: check for null before calling TTY's flush_buffer

[Okash Khawaja]

We should check the flush_buffer method of a tty for null before
invoking it. Some drivers such as usbserial don't implement
flush_buffer. This will be required for upcoming patches where we expand
spk_ttyio to support more than just ttyS*.

Signed-off-by: Okash Khawaja <okash.khawaja@xxxxxxxxx>
Reviewed-by: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>

---
 drivers/staging/speakup/spk_ttyio.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/staging/speakup/spk_ttyio.c
+++ b/drivers/staging/speakup/spk_ttyio.c
@@ -227,7 +227,8 @@ static unsigned char spk_ttyio_in_nowait
 
 static void spk_ttyio_flush_buffer(void)
 {
-	speakup_tty->ops->flush_buffer(speakup_tty);
+	if (speakup_tty->ops->flush_buffer)
+		speakup_tty->ops->flush_buffer(speakup_tty);
 }
 
 int spk_ttyio_synth_probe(struct spk_synth *synth)