ALSA: sgio2audio.c: clean up checking

vfree() does it's own 'NULL' check,so no need for check before
calling it.
Signed-off-by: Figo.zhang <figo1802@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/mips/sgio2audio.c

@@ -619,8 +619,7 @@ static int snd_sgio2audio_pcm_hw_params(struct snd_pcm_substream *substream,
 /* hw_free callback */
 static int snd_sgio2audio_pcm_hw_free(struct snd_pcm_substream *substream)
 {
-	if (substream->runtime->dma_area)
-		vfree(substream->runtime->dma_area);
+	vfree(substream->runtime->dma_area);
 	substream->runtime->dma_area = NULL;
 	return 0;
 }