ALSA: core: check for underflow in snd_pcm_sw_params()

As far as I can see, having an invalid ->tstamp_mode is harmless, but
adding a check silences a static checker warning.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_native.c

@@ -650,7 +650,8 @@ static int snd_pcm_sw_params(struct snd_pcm_substream *substream,
 	}
 	snd_pcm_stream_unlock_irq(substream);
 
-	if (params->tstamp_mode > SNDRV_PCM_TSTAMP_LAST)
+	if (params->tstamp_mode < 0 ||
+	    params->tstamp_mode > SNDRV_PCM_TSTAMP_LAST)
 		return -EINVAL;
 	if (params->proto >= SNDRV_PROTOCOL_VERSION(2, 0, 12) &&
 	    params->tstamp_type > SNDRV_PCM_TSTAMP_TYPE_LAST)