KVM: arm64: Kill fault->ipa

KVM: arm64: Kill fault->ipa

fault->ipa, in a nested contest, represents the output of the guest's
S2 translation for the fault->fault_ipa input, and is equal to
fault->fault_ipa otherwise,

Given that this is readily available from kvm_s2_trans_output(),
drop fault->ipa and directly compute fault->gfn instead, which
is really what we want.

Tested-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>