KVM: x86/mmu: remove unnecessary flush_workqueue()

All work currently pending will be done first by calling destroy_workqueue,
so there is unnecessary to flush it explicitly.
Reported-by: NZeal Robot <zealci@zte.com.cn>
Signed-off-by: NLv Ruyi <lv.ruyi@zte.com.cn>
Reviewed-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20220401083530.2407703-1-lv.ruyi@zte.com.cn>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/tdp_mmu.c

@@ -51,7 +51,7 @@ void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm)
 	if (!kvm->arch.tdp_mmu_enabled)
 		return;
 
-	flush_workqueue(kvm->arch.tdp_mmu_zap_wq);
+	/* Also waits for any queued work items.  */
 	destroy_workqueue(kvm->arch.tdp_mmu_zap_wq);
 
 	WARN_ON(!list_empty(&kvm->arch.tdp_mmu_pages));