ALSA: usb-audio: Choose audioformat of a counter-part substream

The implicit feedback mode needs to handle two endpoints and the
choice of the audioformat object for the sync EP is important since
this determines the compatibility of the hw_params.  The current code
uses the same audioformat object if both the main EP and the sync EP
point to the same iface/altsetting.  This was done in consideration of
the non-implicit-fb sync EP handling, and it doesn't match well with
the cases where actually to endpoints are defined in the sameiface /
altsetting like a few Pioneer devices.

Modify snd_usb_find_implicit_fb_sync_format() to pick up the
audioformat that is assigned in the counter-part substreams primarily,
so that the actual capture stream can be opened properly.  We keep the
same audioformat object only as a fallback in case nothing found,
though.

Fixes: 9fddc15e ("ALSA: usb-audio: Factor out the implicit feedback quirk code")
Link: https://lore.kernel.org/r/20210108075219.21463-3-tiwai@suse.de


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