ALSA: usb-audio: Don't create a mixer element with bogus volume range

Some USB-audio descriptors provide a bogus volume range (e.g. volume
min and max are identical), which confuses user-space.
This patch makes the driver skipping such a control element.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=206221
Link: https://lore.kernel.org/r/20200214144928.23628-1-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer.c

@@ -1666,6 +1666,16 @@ static void __build_feature_ctl(struct usb_mixer_interface *mixer,
 	/* get min/max values */
 	get_min_max_with_quirks(cval, 0, kctl);
 
+	/* skip a bogus volume range */
+	if (cval->max <= cval->min) {
+		usb_audio_dbg(mixer->chip,
+			      "[%d] FU [%s] skipped due to invalid volume\n",
+			      cval->head.id, kctl->id.name);
+		snd_ctl_free_one(kctl);
+		return;
+	}
+
+
 	if (control == UAC_FU_VOLUME) {
 		check_mapped_dB(map, cval);
 		if (cval->dBmin < cval->dBmax || !cval->initialized) {