ufs, msdosfs: do not record witness order when creating vnode

When allocating new vnode, we need to lock it exclusively before
making it externally visible. Since other threads cannot observe the
vnode yet, current lock order cannot create LoR conditions.

Reviewed by: mckusick
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D34126