…y container"

If (for whatever reason) no container uses a claim, then there's no need to
prepare it.

When a second pod wanted to use a claim, the obligatory sanity check whether
the pod is really allowed to use the claim ("reserved for") was skipped.

1aeec10 removed iterating over containers in favor of iterating over pod
claims. This had the unintended consequence that NodePrepareResource gets
called unnecessarily when no container needs the claim. The more natural
behavior is to skip unused resources. This enables (theoretic, at this time)
use cases where some DRA driver relies on the controller part to influence
scheduling, but then doesn't use CDI with containers.