bcache: 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: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/bcache/sysfs.c

@@ -154,7 +154,7 @@ static ssize_t bch_snprint_string_list(char *buf,
 	size_t i;
 
 	for (i = 0; list[i]; i++)
-		out += snprintf(out, buf + size - out,
+		out += scnprintf(out, buf + size - out,
 				i == selected ? "[%s] " : "%s ", list[i]);
 
 	out[-1] = '\n';