ALSA: wavefront - add const

Fix const to non-const pointer cast warning in wavefront_synth.c.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

sound/isa/wavefront/wavefront_synth.c

@@ -1939,7 +1939,7 @@ static int __devinit
 wavefront_download_firmware (snd_wavefront_t *dev, char *path)
 
 {
-	unsigned char *buf;
+	const unsigned char *buf;
 	int len, err;
 	int section_cnt_downloaded = 0;
 	const struct firmware *firmware;