perf tools: Fix time sorting

The final sort might get confused when the comparison is done over
bigger numbers than int like for -s time.

Check the following report for longer workloads:

  $ perf report -s time -F time,overhead --stdio

Fix hist_entry__sort() to properly return int64_t and not possible cut
int.

Fixes: 043ca389

 ("perf tools: Use hpp formats to sort final output")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org # v3.16+
Link: http://lore.kernel.org/lkml/20191104232711.16055-1-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>