perf tools: Use sysfs__mountpoint() when reading cpu topology

perf tools: Use sysfs__mountpoint() when reading cpu topology

Use sysfs__mountpoint() when reading sysfs files to obtain cpu/numa
topologies.

Also use scnprintf instead of sprintf as suggested by Namhyung.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20190219095815.15931-5-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>