ALSA: sound/drivers/vx: fix sparse warning: different signedness

Fix this sparse warning:
  sound/drivers/vx/vx_uer.c:301:42: warning: incorrect type in argument 2 (different signedness)
Signed-off-by: NHannes Eder <hannes@hanneseder.net>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/drivers/vx/vx_uer.c

@@ -103,7 +103,7 @@ static void vx_write_one_cbit(struct vx_core *chip, int index, int val)
  * returns the frequency of UER, or 0 if not sync,
  * or a negative error code.
  */
-static int vx_read_uer_status(struct vx_core *chip, int *mode)
+static int vx_read_uer_status(struct vx_core *chip, unsigned int *mode)
 {
 	int val, freq;