nfs: Fix argument typo to avoid a crash

A typo resulted in the wrong argument for a bytewise
comparison that could result in a crash if
the incorrect argument was not a valid pointer.

This patch fixes the argument.

While investigating this, I noticed that the
correct argument was not being filled in as
required, so this patch fixes that, as well.

Somehow, recovery from a NFSv4.1/4.2 server
crash worked during testing, so this was not
detected. The bug/patch only affects NFS
client mounts using NFSv4.1/4.2.

PR: 294925
Reported by: Jov <amutu@amutu.com>
MFC after: 3 days