KVM: release anon file in failure path of vm creation

The failure of create debugfs of VM will return directly without release
the anon file. It will leak memory and file descriptors, even through
be not serious.

Signed-off-by: Liu Shuo <shuo.a.liu@intel.com>
Fixes: 536a6f88


Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>