ALSA: firewire-lib: add irq_target member into amdtp_domain struct

This commit is a preparation to handle several IR/IT contexts in the same
domain by tasklet context for one of the IT context. Such IT context is
stored to AMDTP domain structure as 'irq_target'.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20191018061911.24909-2-o-takashi@sakamocchi.jp


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