perf top: Filter symbols based on __map__is_kernel(map)

Instead of using dso->kernel, this is equivalent at the moment,
and helps in reducing the accesses to dso->kernel.

Cc: Adrian Hunter <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Wang Nan <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

tools/perf/builtin-top.c

@@ -655,7 +655,7 @@ static int symbol_filter(struct map *map, struct symbol *sym)
 {
 	const char *name = sym->name;
 
-	if (!map->dso->kernel)
+	if (!__map__is_kernel(map))
 		return 0;
 	/*
 	 * ppc64 uses function descriptors and appends a '.' to the