perf test: Use TEST_FAIL in the TEST_ASSERT macros instead of -1

Just to make things clearer, return TEST_FAIL (-1) instead of an open
coded -1.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/ZdepeMsjagbf1ufD@x1