perf test attr: Propagate the return value from the test to the wrapper

Currently it does not matter what the python script actually returns,
the test always passes, as the $err variable is always 0.

Fix that.

Fixes: 8519e4f44c ("perf test: Add a shell wrapper for "Setup struct perf_event_attr"")
Signed-off-by: Michael Petlan <mpetlan@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/shell/attr.sh

@@ -18,5 +18,6 @@ trap trap_cleanup EXIT TERM INT
 shelldir=$(dirname "$0")
 perf_path=$(which perf)
 python "${shelldir}"/lib/attr.py -d "${shelldir}"/attr -v -p "$perf_path"
+err=$?
 cleanup
 exit $err