perf symbols: Use map->prot in place of type==MAP__FUNCTION

Its equivalent, one less use of enum map_type.

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-6m18iv1ty7nh7kxlfmn89sgz@git.kernel.org


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