lockf: correct omission in the usage statement

The -w flag was added without being noted in the usage statement; fix
that now.

While we're here, re-sort the getopt() string.

Reviewed by: 0mp, allanjude, des
Sponsored by: Klara, Inc.

(cherry picked from commit 35095fd23f071d03633312b91a5b460eaf811efa)