perf sort: Check return value of strdup()

perf sort: Check return value of strdup()

When setup_sorting() is called, 'str' is passed to strtok_r() but it's
not checked to have a valid pointer.  As strtok_r() accepts NULL pointer
on a first argument and use the third argument in that case, it can
cause a trouble since our third argument, tmp, is not initialized.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1360130237-9963-3-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>