s390x: fix realize inheritance for kvm-flic

Commit f6f4ce4211 ("s390x: add property adapter_routes_max_batch",
2016-12-09) introduces a common realize (intended to be common for all
the subclasses) for flic, but fails to make sure the kvm-flic which had
its own is actually calling this common realize.

This omission fortunately does not result in a grave problem. The common
realize was only supposed to catch a possible programming mistake by
validating a value of a property set via the compat machine macros. Since
there was no programming mistake we don't need this fixed for stable.

Let's fix this problem by making sure kvm flic honors the realize of its
parent class.

Let us also improve on the error message we would hypothetically emit
when the validation fails.

Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
Fixes: f6f4ce4211 ("s390x: add property adapter_routes_max_batch")
Reviewed-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Reviewed-by: Yi Min Zhao <zyimin@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
