perf kmem: Make it work again on non NUMA machines

perf kmem: Make it work again on non NUMA machines

The commit '2814eb0 perf kmem: Remove die() calls' disabled 'perf kmem'
command for machines without numa support. It made the command fail if
'/sys/devices/system/node' dir wasn't found.

Skipping the numa based initialization in case the directory is not
found and continue execution.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1379003976-5839-5-git-send-email-jolsa@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>