[ALSA] sound/drivers/dummy.c: fix negative snd_pcm_format_width() check

bps is unsigned, a negative snd_pcm_format_width() return value is not noticed
Signed-off-by: Roel Kluin <12o3l@tiscali.nl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/drivers/dummy.c

@@ -230,13 +230,14 @@ static int snd_card_dummy_pcm_prepare(struct snd_pcm_substream *substream)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct snd_dummy_pcm *dpcm = runtime->private_data;
-	unsigned int bps;
+	int bps;
+
+	bps = snd_pcm_format_width(runtime->format) * runtime->rate *
+		runtime->channels / 8;
 
-	bps = runtime->rate * runtime->channels;
-	bps *= snd_pcm_format_width(runtime->format);
-	bps /= 8;
 	if (bps <= 0)
 		return -EINVAL;
+
 	dpcm->pcm_bps = bps;
 	dpcm->pcm_hz = HZ;
 	dpcm->pcm_buffer_size = snd_pcm_lib_buffer_bytes(substream);