KVM doc: Fix KVM_SMI chapter number

The KVM_SMI capability is following the KVM_S390_SET_IRQ_STATE capability
which is "4.95", this changes the number of the KVM_SMI chapter to 4.96.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>