md_ops: correctly adjust the loop parameter in verifyWriterKey
md_ops: correctly adjust the loop parameter in verifyWriterKey

Issue: KBFS-1087

keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs,keybase/client,keybase/client