KVM: PPC: e500: Fix TLBnCFG in KVM_CONFIG_TLB

The associativity, not just total size, can differ from the host
hardware.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>