docs: notifier-error-inject: Correct test's name

Correct test's name for mem-on-off-test.sh/cpu-on-off-test.sh.

Signed-off-by: Zhao Gongyi <zhaogongyi@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>