thunderbolt: Use scnprintf() for avoiding potential buffer overflow

Since snprintf() returns the would-be-output size instead of the
actual output size, the succeeding calls may go beyond the given
buffer limit.  Fix it by replacing with scnprintf().
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/domain.c

@@ -147,10 +147,10 @@ static ssize_t boot_acl_show(struct device *dev, struct device_attribute *attr,
 
 	for (ret = 0, i = 0; i < tb->nboot_acl; i++) {
 		if (!uuid_is_null(&uuids[i]))
-			ret += snprintf(buf + ret, PAGE_SIZE - ret, "%pUb",
+			ret += scnprintf(buf + ret, PAGE_SIZE - ret, "%pUb",
 					&uuids[i]);
 
-		ret += snprintf(buf + ret, PAGE_SIZE - ret, "%s",
+		ret += scnprintf(buf + ret, PAGE_SIZE - ret, "%s",
 			       i < tb->nboot_acl - 1 ? "," : "\n");
 	}