ALSA: usb-audio: Move ITF-USB DSD quirk handling into quirk_flags

The devices with ITF-USB DSD type are listed in another function, and
this can be integrated into the quirk_flags easily.

Link: https://lore.kernel.org/r/20210729073855.19043-8-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>