Mk/bsd.port.mk: Update _PATCH_SEQ to match upstream

Recent upstream change to Mk/bsd.port.mk and Mk/Uses/pathfix.mk, pathfix-pre-patch was renamed to pathfix. Relevant commit here:
https://github.com/freebsd/freebsd-ports/commit/e1fdcabbb7cac0f4c17ed5a7aba8c220d78aeaa1

This broke the ability to compile several ports when using the latest upstream tree, including ftp/curl and audio/flac.