You didn't give much reasoning on why to exclude that row but you can exclude by prtnum
like you've requested:
SELECT i.prtnum, i.lodnum, i.lotnum, i.untqty, i.ftpcod, i.invsts
FROM inventory_view i, locmst m
WHERE i.stoloc = m.stoloc
AND m.arecod = 'PART-HSY'
AND i.prtnum NOT IN(SELECT i2.prtnum FROM inventory_view i2, locmst m2
WHERE i2.stoloc = m2.stoloc AND m2.arecod = 'PART-HSY'
GROUP BY i2.prtnum HAVING COUNT(*) = 1)
ORDER BY i.prtnum