perf sort: Make setup_sorting returns an error code

Currently the setup_sorting() is called for parsing sort keys and exits
if it failed to add the sort key.  As it's included in libperf it'd be
better returning an error code rather than exiting application inside of
the library.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Suggested-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
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/1360130237-9963-2-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/sort.h b/tools/perf/util/sort.h
index e994ad3e..b13e56f 100644
--- a/tools/perf/util/sort.h
+++ b/tools/perf/util/sort.h
@@ -160,7 +160,7 @@
 extern struct sort_entry sort_thread;
 extern struct list_head hist_entry__sort_list;
 
-void setup_sorting(const char * const usagestr[], const struct option *opts);
+int setup_sorting(void);
 extern int sort_dimension__add(const char *);
 void sort_entry__setup_elide(struct sort_entry *self, struct strlist *list,
 			     const char *list_name, FILE *fp);