Fix inconsistency between ptrue and pcmp_* in HVX
Reference issue
What does this implement/fix?
The generic ptrue implementation uses -1 for true value. pcom_* in HVX is changed to uses Scalar(1) for true value in merge_requests 1948. This change fix the inconsistency between them to overload ptrue for HVX to also use Scalar(1) for true value.