KVM: arm64: vgic: Fix locking comment

It is now config_lock that must be held, not kvm lock. Replace the
comment with a lockdep annotation.

Fixes: f0032773 ("KVM: arm64: Use config_lock to protect vgic state")
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/20230518100914.2837292-4-jean-philippe@linaro.org