perf test: test_intel_pt.sh: Fix return checking again

count_result() does not always reset ret=0 which means the value can spill
into the next test result.

Fix by explicitly setting it to zero between tests.

Committer testing:

  # perf test "Miscellaneous Intel PT testing"
  110: Miscellaneous Intel PT testing               : Ok
  #

Tested as well with:

  # perf test -v "Miscellaneous Intel PT testing"

Fixes: fd9b45e3

 ("perf test: test_intel_pt.sh: Fix return checking")
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20221014170905.64069-2-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>