ALSA: snd-usb-caiaq: Correct offset fields of outbound iso_frame_desc

This fixes faulty outbount packets in case the inbound packets
received from the hardware are fragmented and contain bogus input
iso frames. The bug has been there for ages, but for some strange
reasons, it was only triggered by newer machines in 64bit mode.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Reported-and-tested-by: William Light <wrl@illest.net>
Reported-by: Pedro Ribeiro <pedrib@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>