drm/i915/gvt: Unconditionally put reference to KVM when detaching vGPU

Always put the KVM reference when closing a vCPU device, as
intel_vgpu_open_device() succeeds if and only if the KVM pointer is
valid and a reference to KVM is acquired.  And if that doesn't hold true,
the call to kvm_page_track_unregister_notifier() a few lines earlier is
doomed.
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20221111002225.2418386-3-seanjc@google.com

drivers/gpu/drm/i915/gvt/kvmgt.c

@@ -714,15 +714,14 @@ static void intel_vgpu_close_device(struct vfio_device *vfio_dev)
 
 	kvm_page_track_unregister_notifier(vgpu->vfio_device.kvm,
 					   &vgpu->track_node);
+	kvm_put_kvm(vgpu->vfio_device.kvm);
+
 	kvmgt_protect_table_destroy(vgpu);
 	gvt_cache_destroy(vgpu);
 
 	intel_vgpu_release_msi_eventfd_ctx(vgpu);
 
 	vgpu->attached = false;
-
-	if (vgpu->vfio_device.kvm)
-		kvm_put_kvm(vgpu->vfio_device.kvm);
 }
 
 static u64 intel_vgpu_get_bar_addr(struct intel_vgpu *vgpu, int bar)