perf tools: Fix segfault on dynamic entries

perf tools: Fix segfault on dynamic entries

A dynamic entry is created for each tracepoint event.  When it sets up
the sort key, it checks with existing keys using ->equal() callback.
But it missed to set the ->equal for dynamic entries.  The following
segfault was due to the missing ->equal() callback.

  (gdb) bt
  #0  0x0000000000140003 in ?? ()
  #1  0x0000000000537769 in fmt_equal (b=0x2106980, a=0x21067a0) at ui/hist.c:548
  #2  perf_hpp__setup_output_field (list=0x8c6d80 <perf_hpp_list>) at ui/hist.c:560
  #3  0x00000000004e927e in setup_sorting (evlist=<optimized out>) at util/sort.c:2642
  #4  0x000000000043cf50 in cmd_report (argc=<optimized out>, argv=<optimized out>, prefix=<optimized out>)
      at builtin-report.c:932
  #5  0x00000000004865a1 in run_builtin (p=p@entry=0x8bbce0 <commands+192>, argc=argc@entry=7,
      argv=argv@entry=0x7ffd24d56ce0) at perf.c:390
  #6  0x000000000042dc1f in handle_internal_command (argv=0x7ffd24d56ce0, argc=7) at perf.c:451
  #7  run_argv (argv=0x7ffd24d56a70, argcp=0x7ffd24d56a7c) at perf.c:495
  #8  main (argc=7, argv=0x7ffd24d56ce0) at perf.c:620

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1456064558-13086-2-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>