selinux: switch two allocations to use kzalloc_objs()

These were the only two allocations in the policy loading logic
that were not already using kzalloc_objs() for the policy
data structures. Fix these to be consistent with the rest and
to protect against ill-formed policy.

Signed-off-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>