smccc: kvm_guest: Align with DISCOVER_IMPL_CPUS ABI

The ABI of the hypercall requires that R2 and R3 are 0. Explicitly pass
0 for these parameters.

Cc: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Fixes: 86edf6bd ("smccc/kvm_guest: Enable errata based on implementation CPUs")
Reviewed-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Link: https://lore.kernel.org/r/20250327163613.2516073-1-oliver.upton@linux.dev


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>