perf tools: Fix double free in perf test 21 (code-reading.c)

perf_evlist__delete() deletes attached cpu and thread maps
but the test is still using them, so remove them from the
evlist before deleting it.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Link: http://lkml.kernel.org/r/53465E3E.8070201@intel.comSigned-off-by: Jiri Olsa <jolsa@redhat.com>

tools/perf/tests/code-reading.c

@@ -504,6 +504,7 @@ static int do_test_code_reading(bool try_kcore)
 		if (ret < 0) {
 			if (!excl_kernel) {
 				excl_kernel = true;
+				perf_evlist__set_maps(evlist, NULL, NULL);
 				perf_evlist__delete(evlist);
 				evlist = NULL;
 				continue;