firewire: convert sysfs sprintf/snprintf family to sysfs_emit

Fix the following coccicheck warning:

./drivers/firewire/core-device.c:375:8-16: WARNING: use scnprintf or
sprintf.

Reported-by: Abaci <Robot&lt;abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20220615121505.61412-2-o-takashi@sakamocchi.jp


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