perf top: Always sample time to satisfy needs of use of ordered queuing

Bastian reported broken 'perf top -p PID' command, it won't display any
data.

The problem is that for -p option we monitor single thread, so we don't
enable time in samples, because it's not needed.

However since commit 16c66bc1 we use ordered queues to stash data
plus later commits added logic for dropping samples in case there's big
load and we don't keep up. All this needs timestamp for sample. Enabling
it unconditionally for perf top.
Reported-by: Bastian Beischer <bastian.beischer@rwth-aachen.de>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: bastian beischer <bastian.beischer@rwth-aachen.de>
Fixes: 16c66bc1 ("perf top: Add processing thread")
Link: http://lkml.kernel.org/r/20190415125333.27160-1-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-top.c

@@ -1377,6 +1377,7 @@ int cmd_top(int argc, const char **argv)
 			 * */
 			.overwrite	= 0,
 			.sample_time	= true,
+			.sample_time_set = true,
 		},
 		.max_stack	     = sysctl__max_stack(),
 		.annotation_opts     = annotation__default_options,