kunit: Fix KUNIT_SUCCESS() calls in iov_iter tests

kunit: Fix KUNIT_SUCCESS() calls in iov_iter tests

Fix KUNIT_SUCCESS() calls to pass a test argument.

This is a no-op for now because this macro does nothing, but it will be
required for the next commit.

Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: Rae Moar <rmoar@google.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240408074625.65017-6-mic@digikod.net
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>