KVM: arm64: vgic: Fix a comment

It is host userspace, not the guest, that issues
KVM_DEV_ARM_VGIC_GRP_CTRL

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230518100914.2837292-5-jean-philippe@linaro.org