We observed an issue that was some extra columns displayed after switching
perf data file in browser. The steps to reproduce:

1. perf record -a -e cycles,instructions -- sleep 3
2. perf report --group
3. In browser, we use hotkey 's' to switch to another perf.data
4. Now in browser, the extra columns 'Self' and 'Children' are displayed.

The issue is setup_sorting() executed again after repeat path, so dimensions
are added again.

This patch checks the last key returned from __cmd_report(). If it's
K_SWITCH_INPUT_DATA, skips the setup_sorting().

Fixes: ad0de097 ("perf report: Enable the runtime switching of perf data file")
Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Feng Tang <feng.tang@intel.com>
Cc: Jin Yao <yao.jin@intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20191220013722.20592-1-yao.jin@linux.intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>