kvm: book3s: rename lookup_linux_pte() to lookup_linux_pte_and_update()

lookup_linux_pte() is doing more than lookup, updating the pte,
so for clarity it is renamed to lookup_linux_pte_and_update()

Signed-off-by: Bharat Bhushan <bharat.bhushan@freescale.com>
Reviewed-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>