KVM: s390: fix typo in parameter description

Fix typo in parameter description.

Fixes: 8b905d28 ("KVM: s390: provide kvm_arch_no_poll function")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Message-Id: <20190504065145.53665-1-weiyongjun1@huawei.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>