KVM: arm64: Propagate errors from __pkvm_prot_finalize hypercall

KVM: arm64: Propagate errors from __pkvm_prot_finalize hypercall

BugLink: https://bugs.launchpad.net/bugs/1951822
[ Upstream commit 2f2e1a5069679491d18cf9021da19b40c56a17f3 ]

If the __pkvm_prot_finalize hypercall returns an error, we WARN but fail
to propagate the failure code back to kvm_arch_init().

Pass a pointer to a zero-initialised return variable so that failure
to finalise the pKVM protections on a host CPU can be reported back to
KVM.

Cc: Marc Zyngier <maz@kernel.org>
Cc: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211008135839.1193-5-will@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>