perf report: Update column width of dynamic entries

The column width of dynamic entries is updated when comparing hist
entries.  However some unique entries can miss the chance to update.  So
move the update to output resort stage to make sure every entry will get
called before display.

To do that, abuse ->sort callback to update the width when the third
argument is NULL.  When resorting entries in normal path, it never be
NULL so it should be fine IMHO.

Before:

  #       Overhead  ptr / bytes_req / gfp_flags
  # ..............  ..........................................
  #
      37.50%        0xffff8803f7669400
         37.50%        448
            37.50%        GFP_ATOMIC|GFP_NOWARN|GFP_NOMEMALLOC
      10.42%        0xffff8803f766be00
          8.33%        96
             8.33%        GFP_ATOMIC|GFP_NOWARN|GFP_NOMEMALLOC
          2.08%        512
             2.08%        GFP_KERNEL|GFP_NOWARN|GFP_REPEAT|GFP   <-- here

After:

  #       Overhead  ptr / bytes_req / gfp_flags
  # ..............  .....................................................
  #
      37.50%        0xffff8803f7669400
         37.50%        448
            37.50%        GFP_ATOMIC|GFP_NOWARN|GFP_NOMEMALLOC
      10.42%        0xffff8803f766be00
          8.33%        96
             8.33%        GFP_ATOMIC|GFP_NOWARN|GFP_NOMEMALLOC
          2.08%        512
             2.08%        GFP_KERNEL|GFP_NOWARN|GFP_REPEAT|GFP_NOMEMALLOC

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1456512767-1164-5-git-send-email-namhyung@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>