perf ordered-events: Event processing consistency with the regular reader

perf ordered-events: Event processing consistency with the regular reader

Some event processing functions like perf_event__process_tracing_data
return a zero or positive value on success. Ordered event processing
handles any non-zero value as an error, which is inconsistent with
reader__process_events and reader__read_event that only treat negative
values as errors. Make the ordered events error handling consistent
with that of the events reader.

Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>