perf top: Use __map__is_kernel()

Shorter form to figure out if a given map is the kernel one and also
reduces the number of code accessing MAP__{FUNCTION,VARIABLE}, that
should go away at some point.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-rn8pexelsxpx92ce3elu3wiw@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-top.c

@@ -750,7 +750,7 @@ static void perf_event__process_sample(struct perf_tool *tool,
 		machine->kptr_restrict_warned = true;
 	}
 
-	if (al.sym == NULL) {
+	if (al.sym == NULL && al.map != NULL) {
 		const char *msg = "Kernel samples will not be resolved.\n";
 		/*
 		 * As we do lazy loading of symtabs we only will know if the
@@ -764,7 +764,7 @@ static void perf_event__process_sample(struct perf_tool *tool,
 		 * invalid --vmlinux ;-)
 		 */
 		if (!machine->kptr_restrict_warned && !top->vmlinux_warned &&
-		    al.map == machine->vmlinux_maps[MAP__FUNCTION] &&
+		    __map__is_kernel(al.map) &&
 		    RB_EMPTY_ROOT(&al.map->dso->symbols[MAP__FUNCTION])) {
 			if (symbol_conf.vmlinux_name) {
 				char serr[256];