NFSv4: Don't ignore the error return codes from nfs_intent_set_file

If nfs_intent_set_file() returns an error, we usually want to pass that
back up the stack.

Also ensure that nfs_open_revalidate() returns '1' on success.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>