KVM: selftests: Mark test_hv_cpuid_e2big() static in Hyper-V CPUID test

Make the Hyper-V CPUID test's local helper test_hv_cpuid_e2big() static,
it's not used outside of the test (and isn't intended to be).

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20250118003454.2619573-3-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>