ALSA: firewire-lib: fix amdtp_packet tracepoints event for packet_index field

ALSA: firewire-lib: fix amdtp_packet tracepoints event for packet_index field

The snd_firewire_lib:amdtp_packet tracepoints event includes index of
packet processed in a context handling. However in IR context, it is not
calculated as expected.

Cc: <stable@vger.kernel.org>
Fixes: cad95ed94303 ("ALSA: firewire-lib: use packet descriptor for IR context")
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20210513125652.110249-6-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Iwai <tiwai@suse.de>