Ignore errors (wrong usb interface data) found when using the serato
scratch live box with alsa

Thus the alsa controls can be accessed (beware: they don't work though -
but at least it's one ugly error message less)
Signed-off-by: Andreas Bergmeier <lcid-fire@gmx.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>