perf metric: Do not free metric when failed to resolve

perf metric: Do not free metric when failed to resolve

It's dangerous to free the original metric when it's called from
resolve_metric() as it's already in the metric_list and might have other
resources too.  Instead, it'd better let them bail out and be released
properly at the later stage.

So add a check when it's called from metricgroup__add_metric() and
release it.  Also make sure that mp is set properly.

Fixes: aec16d025ee01 ("perf metric: Collect referenced metrics in struct metric_ref_node")
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200915031819.386559-10-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>