[ALSA] usb-audio - Fix AC3 with M-Audio Audiophile USB

Fixed AC3 interface in device_setup=0x00 mode thanks to Hakan
Lennestal and updated documentation

Signed-off-by: Thibault Le Meur <Thibault.LeMeur@supelec.fr>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>