perf python: Decrement the refcount of just created event on failure

perf python: Decrement the refcount of just created event on failure

To avoid a leak if we have the python object but then something happens
and we need to return the operation, decrement the offset of the newly
created object.

Fixes: 377f698db12150a1 ("perf python: Add struct evsel into struct pyrf_event")
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250312203141.285263-5-acme@kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>