perf cpu_map: Use sysfs__read_int in get_{core,socket}_id()

perf cpu_map: Use sysfs__read_int in get_{core,socket}_id()

We have the tools/lib/ sysfs__read_int() for that, avoid code
duplication.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-fqg6vt5ku72pbf54ljg6tmoy@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>