spapr: Get rid of cas_check_pvr() error reporting

spapr: Get rid of cas_check_pvr() error reporting

The cas_check_pvr() function has two purposes:
- finding the "best" logical PVR, ie. the most recent one supported by
  the guest for this CPU type
- checking if the guest supports the real PVR of this CPU type, which
  is just an optional extra information to workaround the lack of
  support for "compat" mode in PR KVM

This logic doesn't need error reporting, really. If we don't find a
suitable logical PVR, we return the special value 0 which is definitely
not a valid PVR. Let the caller decide on whether it should error out
or not.

This doesn't change the behavior.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <20200914123505.612812-6-groug@kaod.org>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>