perf python: Fix thread check in pyrf_evsel__read

JIRA: https://issues.redhat.com/browse/RHEL-78198

upstream
========
commit 64ec9b9
Author: Ian Rogers <irogers@google.com>
Date: Thu Jul 10 16:51:23 2025 -0700

description
===========
The CPU index is incorrectly checked rather than the thread index.

Fixes: 739621f ("perf python: Add evsel read method")
    Signed-off-by: Ian Rogers <irogers@google.com>
    Link: https://lore.kernel.org/r/20250710235126.1086011-11-irogers@google.com
    Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Signed-off-by: Michael Petlan <mpetlan@redhat.com>

Author: rfmvh

tools/perf/util/python.c

@@ -910,7 +910,7 @@ static PyObject *pyrf_evsel__read(struct pyrf_evsel *pevsel,
 		return NULL;
 	}
 	thread_idx = perf_thread_map__idx(evsel->core.threads, thread);
-	if (cpu_idx < 0) {
+	if (thread_idx < 0) {
 		PyErr_Format(PyExc_TypeError, "Thread %d is not part of evsel's threads",
 			     thread);
 		return NULL;