kernel: avoid panic with segio and SG_FAULT segments

kernel: avoid panic with segio and SG_FAULT segments

the problem is that segio doesnt check segment attributes
and it can't really in case of SG_FAULT which can be
inherited from pseg and toggle at any time.

so instead of returning -1 from fault into the fault$cputype
handler which then panics when fault happend kernel mode,
we jump into segio's waserror() block just like in the
demand load i/o error case (faulterror()).