ALSA: firewire: Fix -Wformat-truncation warning for longname string

The filling of card->longname can be gracefully truncated, as it's
only informative.  Use scnprintf() and suppress the superfluous
compile warning with -Wformat-truncation.

Link: https://lore.kernel.org/r/20230915082802.28684-11-tiwai@suse.de


Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Tested-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>