ALSA: control: Allow to pass items zero to snd_ctl_enum_info()

Although this is weird, some drivers want to allow empty control
elements intentionally, e.g. the number of items may change depending
on the firmware status.  Let the function simply returning in such a
case.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/core/control.c

@@ -1745,6 +1745,8 @@ int snd_ctl_enum_info(struct snd_ctl_elem_info *info, unsigned int channels,
 	info->type = SNDRV_CTL_ELEM_TYPE_ENUMERATED;
 	info->count = channels;
 	info->value.enumerated.items = items;
+	if (!items)
+		return 0;
 	if (info->value.enumerated.item >= items)
 		info->value.enumerated.item = items - 1;
 	WARN(strlen(names[info->value.enumerated.item]) >= sizeof(info->value.enumerated.name),