ALSA: usb-audio: Fix potential leak of pd at parsing UAC3 streams

ALSA: usb-audio: Fix potential leak of pd at parsing UAC3 streams

At parsing UAC3 streams, we allocate a PD object at each time, and
either assign or free it.  But there is a case where the PD object may
be leaked; namely, in __snd_usb_parse_audio_interface() loop, when an
audioformat shares the same endpoint with others, it's put to a link
and returns from snd_usb_add_audio_stream(), but the PD is forgotten
afterwards.  Overall, the treatment of PD object in the parser code is
a bit flaky, and we should be more careful about the object ownership.

This patch tries to fix the above case and improve the code a bit.
The pd object is now managed with the auto-cleanup in the loop, and
the ownership is updated when the pd object gets assigned to the
stream, which guarantees the release of the leftover object.

Fixes: 7edf3b5e6a45 ("ALSA: usb-audio: AudioStreaming Power Domain parsing")
Link: https://patch.msgid.link/20260427151508.12544-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>