mnt: typo fix

We only malloc() size amount of space, so we shouldn't snprintf past that.
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

mount.c

@@ -769,7 +769,7 @@ static int resolve_external_mounts(struct mount_info *info)
 		if (!p)
 			return -1;
 
-		ret = snprintf(p, size+1, "%s%s", match->mountpoint + 1, m->root);
+		ret = snprintf(p, size, "%s%s", match->mountpoint + 1, m->root);
 		if (ret < 0 || ret >= size) {
 			free(p);
 			return -1;