coccinelle: skip the xsprintf transformation on man pages

since we don't expose xsprintf to users.

coccinelle/xsprintf.cocci

@@ -1,6 +1,7 @@
 @@
+position p : script:python() { not p[0].file.startswith("man/") };
 expression e, fmt;
 expression list vaargs;
 @@
-- snprintf(e, sizeof(e), fmt, vaargs);
+- snprintf@p(e, sizeof(e), fmt, vaargs);
 + xsprintf(e, fmt, vaargs);