KVM: fix kvm_vm_ioctl_deassign_device

only need to set assigned_dev_id for deassignment, use
match->flags to judge and deassign it.
Acked-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Weidong Han <weidong.han@intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

virt/kvm/kvm_main.c

@@ -517,7 +517,7 @@ static int kvm_vm_ioctl_deassign_device(struct kvm *kvm,
 		goto out;
 	}
 
-	if (assigned_dev->flags & KVM_DEV_ASSIGN_ENABLE_IOMMU)
+	if (match->flags & KVM_DEV_ASSIGN_ENABLE_IOMMU)
 		kvm_deassign_device(kvm, match);
 
 	kvm_free_assigned_device(kvm, match);