KVM: VMX: Stash kvm_vmx in a local variable for Hyper-V paravirt TLB flush

Capture kvm_vmx in a local variable instead of polluting
hv_remote_flush_tlb_with_range() with to_kvm_vmx(kvm).

No functional change intended.

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210305183123.3978098-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>