kvm: fix events.flags (KVM_VCPUEVENT_VALID_SMM) overwritten by 0

Fix events.flags (KVM_VCPUEVENT_VALID_SMM) overwritten by 0.

Signed-off-by: He Rongguang <herongguang.he@huawei.com>
Message-Id: <57E38EAC.3020108@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>