Use of parameterized testing is documented [1] but such use case
is not present in demo kunit test. Add small subtest for that.

[1] https://kernel.org/doc/html/latest/dev-tools/kunit/usage.html#parameterized-testingSigned-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: David Gow <davidgow@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>