perf tools: Update srcline/file if needed

Normally the hist entry's srcline and/or srcfile is set during sorting.
However sometime it's possible to a hist entry's srcline is not set yet
after the sorting.  This is because the entry is so unique and other
sort keys already make it distinct.  Then the srcline/file sort didn't
have a chance to be called during the sorting.  In that case it has NULL
srcline/srcfile field and shows nothing.

Before:

  $ perf report -s comm,sym,srcline
  ...
  Overhead  Command       Symbol
  -----------------------------------------------------------------
    34.42%  swapper       [k] intel_idle          intel_idle.c:0
     2.44%  perf          [.] __poll_nocancel     (null)
     1.70%  gnome-shell   [k] fw_domains_get      (null)
     1.04%  Xorg          [k] sock_poll           (null)

After:

    34.42%  swapper       [k] intel_idle          intel_idle.c:0
     2.44%  perf          [.] __poll_nocancel     .:0
     1.70%  gnome-shell   [k] fw_domains_get      fw_domains_get+42
     1.04%  Xorg          [k] sock_poll           socket.c:0

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 <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1456101111-14400-1-git-send-email-namhyung@kernel.org


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