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

drivers/firewire/core-device.c

@@ -372,8 +372,7 @@ static ssize_t rom_index_show(struct device *dev,
 	struct fw_device *device = fw_device(dev->parent);
 	struct fw_unit *unit = fw_unit(dev);
 
-	return snprintf(buf, PAGE_SIZE, "%d\n",
-			(int)(unit->directory - device->config_rom));
+	return sysfs_emit(buf, "%td\n", unit->directory - device->config_rom);
 }
 
 static struct device_attribute fw_unit_attributes[] = {
@@ -403,8 +402,7 @@ static ssize_t guid_show(struct device *dev,
 	int ret;
 
 	down_read(&fw_device_rwsem);
-	ret = snprintf(buf, PAGE_SIZE, "0x%08x%08x\n",
-		       device->config_rom[3], device->config_rom[4]);
+	ret = sysfs_emit(buf, "0x%08x%08x\n", device->config_rom[3], device->config_rom[4]);
 	up_read(&fw_device_rwsem);
 
 	return ret;