NFSv4.1/flexfiles: Don't mark the entire deviceid as bad for file errors

If the file was fenced and/or has been deleted on the DS, then we want
to retry pNFS after a layoutreturn with error report. If the server
cannot fix the problem, then we rely on it to tell us so in the
response to the LAYOUTGET.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>