perf script: Autopep8 futex-contention

10 years leaves its mark! Python has evolved and so has its style guide.
Even with vim it is getting hard to follow the no longer valid
guidelines (spaces vs. tabs).

Autopep8 this code to modernize it!

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
Link: http://lore.kernel.org/lkml/20200921201928.799498-1-hagen@jauu.net


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