perf symbols: Use __map__is_kernel() instead of ad-hoc equivalent code

perf symbols: Use __map__is_kernel() instead of ad-hoc equivalent code

Shorter, should be equivalent code, use it.

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-q90olng8sfkvrnsrwu7xnul6@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>