perf intel-pt: Fix next 'err' value, walking trace

Code after label 'next:' in intel_pt_walk_trace() assumes 'err' is zero,
but it may not be, if arrived at via a 'goto'. Ensure it is zero.

Fixes: 7c1b16ba ("perf intel-pt: Add support for decoding FUP/TIP only")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: stable@vger.kernel.org # v5.15+
Link: https://lore.kernel.org/r/20211210162303.2288710-6-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/intel-pt-decoder/intel-pt-decoder.c

@@ -2942,6 +2942,7 @@ static int intel_pt_walk_trace(struct intel_pt_decoder *decoder)
 		if (err)
 			return err;
 next:
+		err = 0;
 		if (decoder->cyc_threshold) {
 			if (decoder->sample_cyc && last_packet_type != INTEL_PT_CYC)
 				decoder->sample_cyc = false;