NFSv4: Report the error from nfs4_select_rw_stateid()

In pnfs_update_layout() ensure that we do report any fatal errors from
nfs4_select_rw_stateid().

Fixes: d9aba2b4 ("NFSv4: Don't use the zero stateid with layoutget")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>