perf top: Fix top.call-graph config option reading

When trying to add the "call-graph" variable for top into the
.perfconfig file, like:

      [top]
            call-graph = fp

I that perf_top_config() do not parse this variable.

Fix it by calling perf_default_config() when the top.call-graph variable
is set.
Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: b8cbb349 ("perf config: Bring perf_default_config to the very beginning at main()")
Link: http://lkml.kernel.org/r/1520853957-36106-1-git-send-email-xieyisheng1@huawei.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-top.c

@@ -1223,8 +1223,10 @@ parse_callchain_opt(const struct option *opt, const char *arg, int unset)
 
 static int perf_top_config(const char *var, const char *value, void *cb __maybe_unused)
 {
-	if (!strcmp(var, "top.call-graph"))
-		var = "call-graph.record-mode"; /* fall-through */
+	if (!strcmp(var, "top.call-graph")) {
+		var = "call-graph.record-mode";
+		return perf_default_config(var, value, cb);
+	}
 	if (!strcmp(var, "top.children")) {
 		symbol_conf.cumulate_callchain = perf_config_bool(var, value);
 		return 0;