ALSA: usb-audio: Fake also USB device id when alias is given

Recently snd-usb-audio driver received a new option, quirk_alias, to
allow user to apply the existing quirk for a different device.  This
works for many quirks as is, but some still need more tune-ups:
namely, some quirks check the USB vendor/device IDs in various places,
thus it doesn't work as long as the ID is different from the expected
one.

With this patch, the driver stores the aliased USB ID, so that these
rest quirks per device ID are applied.  The transition to use the
cached USB ID was already done in the past, so what we needed now is
only to overwrite chip->usb_id.

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