ALSA: firewire: Fix -Wformat-truncation warning for MIDI stream names

The compile warnings at filling MIDI stream name strings are all
false-positive; the number of streams can't go so high.

For suppressing the warning, replace snprintf() with scnprintf().
As stated in the above, truncation doesn't matter.

Link: https://lore.kernel.org/r/20230915082802.28684-12-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>