perf top: Set the 'session_done' volatile variable when exiting

perf top: Set the 'session_done' volatile variable when exiting

So we can get out of hist processing ASAP on user request.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/n/tip-r8aufbgbixr2f85s3wcoaw9v@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>