sound: oss/sb_audio: prevent divide by zero bug

Speed comes from get_user() in audio_ioctl().  We use it to set the "s"
variable before clamping it to valid values so it could lead to a divide
by zero bug.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/oss/sb_audio.c

@@ -575,13 +575,15 @@ static int jazz16_audio_set_speed(int dev, int speed)
 	if (speed > 0)
 	{
 		int tmp;
-		int s = speed * devc->channels;
+		int s;
 
 		if (speed < 5000)
 			speed = 5000;
 		if (speed > 44100)
 			speed = 44100;
 
+		s = speed * devc->channels;
+
 		devc->tconst = (256 - ((1000000 + s / 2) / s)) & 0xff;
 
 		tmp = 256 - devc->tconst;