pnfs: fix bad error handling in send_layoutget

Currently, the code will clear the fail bit if we get back a fatal
error. I don't think that's correct -- we want to clear that bit
if we do not get a fatal error.

Fixes: 0bcbf039

 (nfs: handle request add failure properly)
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>