perf report: Fix a no annotate browser displayed issue

perf report: Fix a no annotate browser displayed issue

When enabling '-b' option in perf record, for example,

  perf record -b ...
  perf report

and then browsing the annotate browser from perf report (press 'A'), it
would fail (annotate browser can't be displayed).

It's because the '.add_entry_cb' op of struct report is overwritten by
hist_iter__branch_callback() in builtin-report.c. But this function doesn't do
something like mapping symbols and sources. So next, do_annotate() will return
directly.

        notes = symbol__annotation(act->ms.sym);
        if (!notes->src)
                return 0;

This patch adds the lost code to hist_iter__branch_callback (refer to
hist_iter__report_callback).

v2:

Fix a crash bug when perform 'perf report --stdio'.

The reason is that we init the symbol annotation only in browser mode, it
doesn't allocate/init resources for stdio mode.

So now in hist_iter__branch_callback(), it will return directly if it's not in
browser mode.

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1514284963-18587-1-git-send-email-yao.jin@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>