KVM: x86: hyper-v: Rename vcpu_to_hv_syndbg() to to_hv_syndbg()

vcpu_to_hv_syndbg()'s argument is  always 'vcpu' so there's no need to have
an additional prefix. Also, this makes the code more consistent with
vmx/svm where to_vmx()/to_svm() are being used.

No functional change intended.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210126134816.1880136-8-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>