perf tools: Align buildid list output for short build ids

With shorter md5 build ids we need to align their paths properly with
other build ids:

  $ perf buildid-list
  17f4e448cc746582ea1881528deb549f7fdb3fd5 [kernel.kallsyms]
  a50e350e97c43b4708d09bcd85ebfff7         .../tools/perf/buildid-ex-md5
  1805c738c8f3ec0f47b7ea09080c28f34d18a82b /usr/lib64/ld-2.31.so
  $

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20201013192441.1299447-9-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>