perf tools: Sync hashmap.h with libbpf's

To pick up the changes in:

  b2f9f153

 ("libbpf: Fix libbpf hashmap on (I)LP32 architectures")

Silencing this warning:

  Warning: Kernel ABI header at 'tools/perf/util/hashmap.h' differs from latest version at 'tools/lib/bpf/hashmap.h'
  diff -u tools/perf/util/hashmap.h tools/lib/bpf/hashmap.h

I'll eventually update the warning to remove the "Kernel ABI" part
and instead state libbpf when noticing that the original is at
"tools/lib/something".

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andriin@fb.com>
Cc: Jakub Bogusz <qboosh@pld-linux.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Ian Rogers <irogers@google.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>