perf tests: Set evlist of test__basic_mmap() to !overwrite

In this test, a large ring buffer is required so all events can feed
into, so overwrite or not is meaningless.

Change to !overwrite so following commits can remove this argument.
Signed-off-by: NWang Nan <wangnan0@huawei.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20171113013809.212417-5-wangnan0@huawei.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/mmap-basic.c

@@ -94,7 +94,7 @@ int test__basic_mmap(struct test *test __maybe_unused, int subtest __maybe_unuse
 		expected_nr_events[i] = 1 + rand() % 127;
 	}
 
-	if (perf_evlist__mmap(evlist, 128, true) < 0) {
+	if (perf_evlist__mmap(evlist, 128, false) < 0) {
 		pr_debug("failed to mmap events: %d (%s)\n", errno,
 			 str_error_r(errno, sbuf, sizeof(sbuf)));
 		goto out_delete_evlist;