perf tools: Correct title markers for asciidoctor

perf tools: Correct title markers for asciidoctor

I've tested to process the perf man pages with asciidoctor that is
picker than asciidoc, and it revealed minor syntax errors in some
documents.  Namely, the title markers aren't aligned with the previous
line, hence asciidoctor didn't recognize as titles.

This patch corrects these markers to be processed properly.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180307105441.28512-1-tiwai@suse.de
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>