KVM: SVM: rename a variable in the svm_create_vcpu

The 'page' is to hold the vcpu's vmcb so name it as such to
avoid confusion.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Message-Id: <20200827171145.374620-2-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>