tools/perf/build: Simplify the autodep inclusion rule

Namhyung Kim noticed that the autodep .d file inclusion rule was
unnecessarily complicated:

  > > +-include *.d */*.d
  >
  > Hmm.. this */*.d part is really needed?

Only include *.d files.

Reported-by: Namhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>