kvmclock: run KVM_KVMCLOCK_CTRL ioctl in vcpu thread

kvmclock: run KVM_KVMCLOCK_CTRL ioctl in vcpu thread

According to KVM API Documentation, we should only
run vcpu ioctls from the same thread that was used
to create the vcpu. This patch makes KVM_KVMCLOCK_CTRL
ioctl consistent with the Documentation.

No functional change.

Signed-off-by: Yongji Xie <xieyongji@baidu.com>
Signed-off-by: Chai Wen <chaiwen@baidu.com>
Message-Id: <1531315364-2551-1-git-send-email-xieyongji@baidu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Yongji Xie <elohimes@gmail.com>