KVM: x86: MMU: make array audit_point_name static

The array audit_point_name is local to the source and does not need to
be in global scope, so make it static.

Cleans up sparse warning:
arch/x86/kvm/mmu_audit.c:22:12: warning: symbol 'audit_point_name' was
not declared. Should it be static?

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>