ALSA: snd-usb-audio: Skip un-parseable mixer units instead of erroring

Some interfaces reference endpoints which do not exists. To
accomodate these, do not fail completely, but skip over them.

This allows the Electrix Ebox-44 with earlier firmware to be
detected and used for audio.
Signed-off-by: Mark Hills <mark@pogo.org.uk>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer.c

@@ -1388,7 +1388,7 @@ static int parse_audio_mixer_unit(struct mixer_build *state, int unitid, void *r
 	for (pin = 0; pin < input_pins; pin++) {
 		err = parse_audio_unit(state, desc->baSourceID[pin]);
 		if (err < 0)
-			return err;
+			continue;
 		err = check_input_term(state, desc->baSourceID[pin], &iterm);
 		if (err < 0)
 			return err;