perf bench futex: Fix lock-pi help string

Obvious copy/paste typo from the requeue program.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Davidlohr Bueso <dbueso@suse.de>
Link: http://lkml.kernel.org/r/1481830584-30909-1-git-send-email-dave@stgolabs.net


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>