perf record: Fix s390 undefined record__auxtrace_init() return value

Command 'perf record' calls:

  cmd_report()
    record__auxtrace_init()
       auxtrace_record__init()

On s390 function auxtrace_record__init() returns random return value due
to missing initialization.

This sometime causes 'perf record' to exit immediately without error
message and creating a perf.data file.

Fix this by setting error the return code to zero before returning from
platform specific functions which may not set the error code in call
cases.
Signed-off-by: NThomas Richter <tmricht@linux.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Link: http://lkml.kernel.org/r/20180423142940.21143-1-tmricht@linux.ibm.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/arch/s390/util/auxtrace.c

@@ -87,6 +87,7 @@ struct auxtrace_record *auxtrace_record__init(struct perf_evlist *evlist,
 	struct perf_evsel *pos;
 	int diagnose = 0;
 
+	*err = 0;
 	if (evlist->nr_entries == 0)
 		return NULL;