fix: Follow pr_regexp_alloc()'s itnerface change on proftpd-v1.3.4

`regex_t *pr_regexp_alloc(void)` was changed to  `regexp.h:pr_regex_t *pr_regexp_alloc(module *m)`

refs http://svn.dd-wrt.com/changeset/17876/src/router/proftpd/modules/mod_auth_file.c