ALSA: usb-audio: Fix Oops by composite quirk enhancement

The quirk argument itself was used as iterator, so it cannot be taken
back to the original value, obviously.

Fixes: d4b8fc66 ('ALSA: usb-audio: Allow multiple entries for the same iface in composite quirk')
Signed-off-by: Takashi Iwai <tiwai@suse.de>